Thursday, 21 July 2016

PHE publishes new advice on vitamin D. Should we all take 10 micrograms per day Vit D all year?

crabsallover says "180 x 25 micrograms Vitamin D tablets cost less than £10 - this is sufficient to supplement Vitamin D levels for a year at 10 micrograms Vitamin D per day".

Public Health England (PHE) is advising today (21st July 2016) that 10 micrograms of vitamin D are needed daily to help keep healthy bones, teeth and muscles.

This advice is based on the recommendations of the Scientific Advisory Committee on Nutrition (SACN) following its review of the evidence on vitamin D and health.

Vitamin D is made in the skin by the action of sunlight and this is the main source of vitamin D for most people. SACN could not say how much vitamin D is made in the skin through exposure to sunlight, so it is therefore recommending a daily dietary intake of 10 micrograms.  PHE advises that in spring and summer, the majority of the population get enough vitamin D through sunlight on the skin and a healthy, balanced diet. During autumn and winter, everyone will need to rely on dietary sources of vitamin D. Since it is difficult for people to meet the 10 microgram recommendation from consuming foods naturally containing or fortified with vitamin D, people should consider taking a daily supplement containing 10 micrograms of vitamin D in autumn and winter.

People whose skin has little or no exposure to the sun, like those in institutions such as care homes, or who always cover their skin when outside, risk vitamin D deficiency and need to take a supplement throughout the year.

Vitamin D regulates the amount of calcium and phosphate in the body, both needed for healthy bones, teeth and muscles. It is found naturally in a small number of foods including oily fish, red meat, liver and egg yolks and in fortified food like breakfast cereals and fat spreads.


The latest data from the PHE National Diet and Nutrition Survey (2008 to 2012) shows that 23% of adults aged 19 to 64 years, 21% of adults aged 65 years and above and 22% of children aged 11 to 18 years have low levels of vitamin D in their blood. This is not the same as having a deficiency, where you would be unwell, but rather means that you are at greater risk of developing a deficiency. If a person is deficient of vitamin D they will be clinically unwell and will need to be treated by a doctor.

PHE recommends against people using sunbeds because extreme short-term use could cause severe burning and long-term damage to the skin, with a possible increased risk of developing skin cancer.

SACN reviewed the evidence on vitamin D and health outcomes. In addition to musculoskeletal health, SACN reviewed the relationship between vitamin D and non-musculoskeletal health outcomes including cancer, Type 1 diabetes, multiple sclerosis and heart disease but found insufficient evidence to draw any firm conclusions.

The recommendations refer to average intake over a period of time, such as one
week, and take account of day-to-day variations in vitamin D intake. Vitamin D plays an important role in the regulation of calcium and phosphate in the body. It is therefore essential for bone health. Without adequate vitamin D, bones can become thin, brittle and mis-shapen.  In extreme cases this can lead to rickets in children, a condition involving a softening of the bones that can lead to fractures and deformity. In adults softening of the bones is called osteomalacia, and may cause pain and muscle weakness.

From the full report:
S.25 Mean dietary intakes of vitamin D from all sources (including supplements) were: 2-4 µg/d (80-160 IU/d) for ages 1.5-64y; 5 µg/d (200 IU/d) for adults aged = 65y.

S.28 For all age groups in the UK, mean plasma 25(OH)D concentration was lowest in winter and highest in summer. Around 30-40% of the population had a plasma 25(OH)D concentration < 25 nmol/L in winter compared to 2-13% in the summer. A large proportion of some population groups did not achieve a plasma/serum 25(OH)D concentration = 25 nmol/L in summer (17% of adults in Scotland; 16% of adults in London; 53% of women of South Asian ethnic origin in Southern England; and 29% of pregnant women in NW London).

Metabolism S.5 Vitamin D is converted to its active metabolite, 1,25-dihydroxyvitamin D (1,25(OH)2D), in two hydroxylation steps. The first hydroxylation is in the liver, where vitamin D is converted to 25- hydroxyvitamin D (25(OH)D), which is the major circulating metabolite of vitamin D and is widely used as a biomarker of vitamin D status; the second hydroxylation is in the kidney where 25(OH)D is converted to 1,25(OH)2D.

The proportion of the population (by age) with a plasma 25(OH)D concentration < 25 nmol/L was: 2-8%, 5m-3y; 12-16%, 4-10y; 20-24%, 11-18y; 22-24%, 19-64y; 17-24%, = 65y and above.

S.7 At latitudes below 37 degrees North, UVB radiation is sufficient for year round vitamin D synthesis. At higher latitude, vitamin D is not synthesised during the winter months. In the UK, sunlight-induced vitamin D synthesis is only effective between late March/early April and September and not from October onwards throughout the winter months.


NHS Choices - report on what the papers say

PHE advice is detailed on NHS choices.  (but was this page really updated on 18/02/2015?)
SACN’s Vitamin D and Health report (300 pages) published 21 July 2016 (pdf)
SACN press release on the vitamin D report (PDF195KB2 pageswhich highlights the report’s main findings and recommendations.
View documents related to the consultation on the draft report.These documents include a substantial number of consultation comments received by SACN, as well as SACN’s response to these comments.

Above report edited by crabsallover from:

Sunday, 19 June 2016

Coffee's cancer risk downgraded (as long as you don't drink it hot)

reposted from:
crabsallover highlightskey pointscomments / links.

A review by the International Agency for Research on Cancer (IARC) concluded that only beverages consumed at higher than 65C posed a possible cancer risk.

Thursday June 16 2016
Letting drinks cool is a good idea
Coffee's cancer risk has now been degraded
"Very hot drinks may cause cancer, but coffee does not, says WHO," The Guardian reports.
A review by the International Agency for Research on Cancer (IARC) concluded that only beverages consumed at higher than 65C posed a possible cancer risk.
The working group's report re-evaluated the cancer-causing properties of drinking coffee, maté (a South American drink), and very hot beverages.
Coffee was classified as a possible cause of cancer in 1991, but the group has cleared the previous classification and suggested any suspected link was because of the hot temperature of the drink.
The researchers concluded there was limited evidence that drinking coffee and maté causes cancer, but say the risk of cancer of the oesophagus – the gullet – may increase with the temperature of the drink above 65C (149F).
Both the Daily Mirror and Daily Mail covered the story. The Mirror reports that leaving your cup of tea for around five minutes should cool it to a safe level.
The Mail reports that, not entirely surprisingly, store-bought black coffee is hot, at between 66 and 81C. So again, it is best left to cool for a while.
As it stands, smoking or alcohol consumption pose a bigger – and better documented – risk for oesophageal cancer.

So what's the matter with maté?

Maté is probably best described as the South American version of "builder's tea".
It is a caffeine-rich concoction served in very hot water and drunk through a metal straw. 

Who produced the report?

The report was published by an international collaboration of researchers (working group) of the IARC, a specialised cancer agency of the World Health Organization (WHO).
The group came together in France as part of the IARC Monographs Programme, which seeks to evaluate and identify environmental factors that can increase the risk of human cancer.
The researchers reviewed epidemiological studies of exposure to carcinogens in human populations, and used the evidence to classify potential hazards as:
  • group 1 – carcinogenic to humans
  • group 2A – probably carcinogenic
  • group 2B – possibly carcinogenic
  • group 3 – not classifiable (no evidence to make a reliable judgement)
  • group 4 – probably not carcinogenic
However, the classification does not indicate what level of risk is associated with the exposure to a classified hazard.
For example, smoking cigarettes and using a sunbed are both group 1 hazards. But the risk of cancer associated with smoking cigarettes is far higher than using a sunbed.
Overall, the exact method of how the authors identified and selected the research is unclear. As such, it's not possible to say that this was a systematic review.
The monographs are published so they can be used by national health agencies to support their actions in preventing exposure to potential carcinogens.

What did the report find?

As part of their re-evaluation, the group assessed more than 1,000 observational and experimental studies.
They concluded:
  • coffee drinking was "not classifiable as to its carcinogenicity to humans" (group 3)
  • maté was "not classifiable as to its carcinogenicity to humans" (group 3)
  • hot drinks above 65C were "probably carcinogenic to humans" (group 2A)


Coffee drinking was evaluated by the IARC in 1991, and at the time was classified as "possibly carcinogenic to humans" (group 2B).
However, this was based on "limited evidence" – defined on the basis that a positive association between hazard and outcome was observed, but bias could not be ruled out.
The current evaluation has been conducted on a much stronger and larger body of evidence, with nearly 500 relevant epidemiological studies identifying more than 20 different cancers.
The group assessed a collection of epidemiological evidence, and gave the greatest weight to prospective cohort and population-based case control studies that had controlled for other exposures, such as tobacco and alcohol consumption.
The studies followed cohorts of people who self-reported their coffee drinking habits to see how many individuals developed cancer and how it was related to their consumption of coffee.
During this re-evaluation, the majority of epidemiological studies showed no association between coffee drinking and cancers of the pancreas, female breast, and prostate. Reduced risks were observed for liver and endometrial cancers.
On judging the various studies, the group concluded the evidence for "coffee drinking causing cancer" was inadequate. Reasons included insufficient data, inconsistency of findings, inadequate control of potential confounders, and bias.


Maté is a hot drink consumed in South America, and is also the national drink of Argentina.
It's a caffeine-rich infusion made from dried leaves of the yerba maté plant. In 1991 the IARC classified it as "probably carcinogenic to humans" (group 2A).
Since then, several epidemiological studies have been conducted evaluating the risk of oesophageal cancer and the consumption of hot maté.
With this new data, the IARC wanted to better understand whether the associations from previous studies were the result of maté itself or the hot temperatures at which it is usually consumed.
The studies found cancer of the oesophagus was associated with drinking hot maté, rather than maté at warm or cold temperatures.

Hot drinks

The findings from the evaluations of maté led the researchers to assess the association between oesophageal cancer and other hot drinks.
Previous research from China, Iran, Japan and Turkey also found the risk of cancer may increase with the temperature of the drink.
The IARC conducted a combined analysis on several epidemiological studies that had assessed the effect of both temperature and the amount of maté consumed on 1,400 patients with oesophageal cancer.
The results showed that regardless of the amount consumed, the risk of cancer increased with an increase in temperature.
There were significant differences in the results from drinking very hot maté, but not with warm maté.
The studies suggested the carcinogenic effects occur when drinking at temperatures above 65C.

What are the implications?

The IARC monographs seek to identify potential cancer hazards to raise awareness that a certain exposure can cause cancer in exposed people. However, they don't issue recommendations.
Their assessment of scientific evidence is produced so the World Health Organization, health agencies and governments can take it into consideration when developing health policies and guidelines. Whatever actions are taken as a result remain in the hands of the authorities concerned.
Professor Tim Underwood, associate professor in surgery at the University of Southampton, said: "The bottom line here is that drinking very hot liquids is a cause of squamous cell cancer of the oesophagus, but the IARC classification can't tell us anything about the size of the risk – so we shouldn't take from this that there's a high risk of developing oesophageal cancer after drinking very hot drinks."
Professor Sir David Spiegelhalter, Winton professor of the public understanding of risk at the University of Cambridge, said: "Last year the IARC said that bacon is carcinogenic, but it became clear that when eaten in moderation it is not very risky.
"In the case of very hot drinks, the IARC conclude they are probably hazardous, but can't say how big the risk might be. This may be interesting science, but makes it difficult to construct a sensible response."
Arguably, a commonsense approach would be to not drink anything hot enough to give you a serious burn if you spilt it on yourself, whether it's maté, coffee or tea.
Analysis by Bazian. Edited by NHS ChoicesFollow NHS Choices on TwitterJoin the Healthy Evidence forum.
Analysis by Bazian
Edited by NHS Choices

Links to the headlines

Cancer risk from coffee downgraded. BBC News, June 15 2016

Links to the science

The International Agency for Research on Cancer Monograph Working Group. Carcinogenicity of drinking coffee, maté, and very hot beverages. The Lancet Oncology. Published online June 15 2016

Further reading

International Agency for Research on Cancer. Q&A on Monographs Volume 116: Coffee, maté, and very hot beverages (PDF, 65kb). June 2016

News analysis: Does the 5:2 fast diet work? (May 2013 update)

reposted without editing from:
crabsallover highlightskey pointscomments / links.

This is an update of a January 2013 NHS Choices article - see here.

Monday January 14 2013

Is intermittent fasting right for you?
Note – this article, originally written in January 2013, was updated in May 2013.
The 5:2 diet is an increasingly popular diet plan with a flurry of newspaper articles and books being published on it in the run up to Christmas 2012 and in January 2013.
The diet first reached the mainstream via a BBC Horizon documentary called Eat, Fast and Live Longer, broadcast in August 2012.
The 5:2 diet is based on a principle known as intermittent fasting (IF) – where you eat normally at certain times and then fast during other times.
The 5:2 diet is relatively straightforward – you eat normally five days a week, and fast on the other two days.

What does a daily 600-calorie diet look like?

A 600-calorie diet could consist of a slice of ham and two scrambled eggs for breakfast and then some grilled fish and vegetables for your evening meal. And of course nothing but water, black coffee and/or green tea to drink.
Champions of the 5:2 diet claim that other than helping people lose weight, 5:2 diet can bring other significant health benefits, including:
  • increased lifespan
  • improved cognitive function and protection against conditions such as dementia and Alzheimer’s disease
  • protection from disease
However the body of evidence about 5:2 diet and intermittent fasting is limited when compared to other types of weight loss techniques. 

What we don’t know about intermittent fasting

Despite its increasing popularity, there is a great deal of uncertainty about IF with significant gaps in the evidence.
For example, it is unclear:
  • what pattern of IF is the most effective in improving health outcomes – 5:2, alternative day fasting, or something else entirely different
  • what is the optimal calorie consumption during the fasting days – the 5:2 diet recommends 500 calories for women and 600 for men, but these recommendations seem arbitrary without clear evidence to support them
  • how sustainable is IF in the long-term – would most people be willing to stick with the plan for the rest of their lives?

Are there any side effects from intermittent fasting?

Little is known about possible side effects as no systematic attempt has been made to study this issue. Anecdotal reports of effects include:
  • difficulties sleeping
  • bad breath (a known problem with low carbohydrate diets)
  • irritability
  • anxiety
  • dehydration
  • daytime sleepiness
However, more research would be needed to confirm these side effects and their severity.
If you are fasting, you may want to think about how fasting will impact on your life during your fasting days. You are likely to be very hungry and have less energy and this could affect your ability to function (such as at work), in particular it may affect your ability to exercise which is an important part of maintaining a healthy weight.
Also, IF may not be suitable for pregnant women and people with specific health conditions, such as diabetes, or a history of eating disorders.
Because it is a fairly radical approach to weight loss, if you are considering trying IF for yourself, it is wise to speak to your GP first to see if it is safe to do so.

Evidence about the 5:2 diet

Despite its popularity evidence directly assessing the 5:2 model of intermittent fasting is limited.
But since this article was originally written in January 2013 we have been alerted to research, led by Dr Michelle Harvie, which did look at the 5:2 model.
In one study carried out in 2010 the researchers did find that women placed on a 5:2 diet achieved similar levels of weight loss as women placed on a calorie-controlled diet.
They also experienced reductions in a number of biological indicators (biomarkers) that suggest a reduction in the risk of developing chronic diseases such as type 2 diabetes.
further study in 2012 suggested that the 5:2 model may help lower the risk of certain obesity-related cancers, such as breast cancer.
The increasing popularity of the 5:2 diet should lead to further research of this kind.

Evidence about other forms of IF

There is some degree of evidence about the potential benefits of other forms of IF – albeit with some limitations.
It should be stressed that our assessment of the evidence was confined to entering a number of keywords into Google Scholar and then looking at a small number of studies which we felt would be useful to explore further.
We did not carry out a systematic review (though arguably, it would be useful for researchers to do so). So the information provided below should be taken in the spirit of us trying to provide an introduction to some of the evidence and science of IF – not an exhaustive "last word" on the topic.
Is there any evidence that intermittent fasting aids weight loss?
One of the most recent pieces of research on intermittent fasting is a2012 study (PDF, 291kb) that recruited 30 obese women known to have pre-existing risk factors for heart disease.
After an initial two-week period they were then given a combination diet of low-calorie liquid meals for six days of a week (similar to Slim Fast diet products) and then asked to fast for one day a week (comsuming no more than 120 calories).
After eight weeks, on average, the women lost around 4kg (8.8lb) in weight and around 6cm (2.3 inches) off their waist circumference.
However, there are a number of limitations to consider when looking at this as evidence that it might be a generally beneficial thing to do for most ordinary people, including that:
  • These women may have had increased motivation to stick with the diet because they knew their weight would be monitored (this is a psychological effect that slimming clubs make use of).
  • The women had been told that they were at risk of heart disease. It is uncertain how well most of us would cope with such an extreme diet.
  • The follow-up period was short – just two months. It is not clear whether this diet would be sustainable in the long term or whether it could cause any side effects.
  • 30 people is quite a small sample size. A much larger sample – including men – is required to see if intermittent fasting would be effective in most overweight or obese people.
Is there any evidence intermittent fasting increases lifespan?
There is quite a wide range of work on the effects of IF on combating the effects of ageing, but almost all of these studies involved either rats, mice or monkeys. One big problem with studies in animals – particularly rodents – is that they are only expected to live for a few years. While this makes them ideal subjects for longevity studies, carrying out similar, more useful experiments in humans, requires decades-long research to gain credible results.
In an unsystematic look at the evidence, we find only one study involving humans: a 2006 review (PDF, 65kb) of an experiment actually carried out in 1957 in Spain.
In this 1957 study, 120 residents of an old people’s home were split into two groups (it is unclear from the study whether this was done at random). The first group (the control group) ate a normal diet. The second group (the IF group) ate a normal diet one day and then a restricted diet (estimated to be around 900 calories) the next.
After three years there were 13 deaths in the control group and only six deaths in the IF group.
This study is again limited by the small sample size meaning that the differences in death are more likely to be the results of a statistical fluke. Also, many experts would feel uneasy about issuing dietary guidelines based on a study over half a century old with unclear methods. It is unlikely that this experiment could be repeated today – denying food to elderly people in residential care is unlikely to be looked at kindly by an ethics committee.
Is there any evidence intermittent fasting prevents cognitive decline?
It seems that all of the studies on the supposed protective effects of IF against conditions that can cause a decline in cognitive function (such as dementia or Alzheimer’s disease) involve animals.
For example, a 2006 study (PDF, 843kb) involved mice that had been genetically engineered to develop changes in brain tissue similar to those seen in people with Alzheimer’s disease.
Mice on an IF diet appeared to experience a slower rate of cognitive decline than mice on a normal diet (cognitive function was assessed using a water maze test).
While the results of these animals tests are certainly intriguing, animal studies have inherent limitations. We can never be sure that the results will be applicable in humans.
Is there any evidence that intermittent fasting prevent diseases?
Much of the published research into the potential preventative effects of IF involve measuring biological markers associated with chronic disease, such as insulin-like growth factor-I (IGF-I) – known to be associated with cancer.
Using these kinds of biological surrogates is a legitimate way to carry out research, but they do not guarantee successful real-world outcomes.
For example, some medications that were found to lower blood pressure readings taken in laboratory conditions failed to prevent strokes once they had been introduced for use in the healthcare of patients in the world.
2007 clinical review (PDF, 119kb) looking at the effects of IF in humans in terms of real-world health outcomes concluded that IF (specifically, alternative day fasting) may have a protective effect against heart disease, type 2 diabetes and cancer. However, it concluded "more research is required to establish definitively the consequences of ADF (alternative day fasting)".


Compared to other types of weight loss programmes the evidence base of the safety and effectiveness of the 5:2 diet is limited.
If you are considering it then you should first talk to your GP to see if it is suitable for you. Not everyone can safely fast.
Other methods of weight loss include:
Find recommended, simple, low cost ways to lose weight in the Live Well: lose weight pages.
Edited by NHS Choices

Links to the headlines

The power of intermittent fasting. BBC News, August 5 2012

Links to the science

Harvie M, Howell A. Energy restriction and the prevention of breast cancer. Proceedings of the Nutrition Society. Published online March 12 2012
Harvie M, Pegington M, Mattson MP, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomised trial in young overweight women. International Journal of Obesity. Published online October 5 2010
Varady KA, Hellerstein MK, et al. Alternate-day fasting and chronic disease prevention: a review of human and animal trials (PDF, 118.6KB). American Journal of Clinical Nutrition. Published online 2007     

Friday, 27 May 2016

Physical activity guidelines for adults

How much physical activity do adults aged 19-64 years old need to do to stay healthy?
To stay healthy or to improve health, adults need to do two types of physical activity each week: aerobic and strength exercises.
How much physical activity you need to do each week depends on your age. Click on the links below for the recommendations for other age groups:

Guidelines for adults aged 19-64

To stay healthy, adults aged 19-64 should try to be active daily and should do:
  • at least 150 minutes of moderate aerobic activity such as cycling or fast walking every week, and  
  • strength exercises on two or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms).  
  • 75 minutes of vigorous aerobic activity, such as running or a game of singles tennis every week, and
  • strength exercises on two or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms). 
  • A mix of moderate and vigorous aerobic activity every week. For example, two 30-minute runs plus 30 minutes of fast walking equates to 150 minutes of moderate aerobic activity, and
  • strength exercises on two or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms).  
A rule of thumb is that one minute of vigorous activity provides the same health benefits as two minutes of moderate activity.  
One way to do your recommended 150 minutes of weekly physical activity is to do 30 minutes on 5 days a week. 
All adults should also break up long periods of sitting with light activity. Find out why sitting is bad for your health.

What counts as moderate aerobic activity?

Examples of activities that require moderate effort for most people include:
  • walking fast
  • water aerobics
  • riding a bike on level ground or with few hills
  • doubles tennis
  • pushing a lawn mower
  • hiking
  • skateboarding
  • rollerblading
  • volleyball
  • basketball 
Moderate activity will raise your heart rate and make you breathe faster and feel warmer. One way to tell if you're working at a moderate level is if you can still talk, but you can't sing the words to a song.

What counts as vigorous activity?

There is good evidence that vigorous activity can bring health benefits over and above that of moderate activity.
Examples of activities that require vigorous effort for most people include:
Vigorous activity makes you breathe hard and fast. If you're working at this level, you won't be able to say more than a few words without pausing for breath.
In general, 75 minutes of vigorous activity can give similar health benefits to 150 minutes of moderate activity.
For a moderate to vigorous workout, try Couch to 5K, a nine-week running plan for beginners.

What activities strengthen muscles?

Muscle strength is necessary for:
  • all daily movement
  • to build and maintain strong bones
  • to regulate blood sugar and blood pressure
  • to help maintain a healthy weight
Muscle-strengthening exercises are counted in repetitions and sets. A repetition is one complete movement of an activity, like a bicep curl or a sit-up. A set is a group of repetitions.
For each strength exercise, try to do:
  • at least one set
  • eight to 12 repetitions in each set 
To get health benefits from strength exercises, you should do them to the point where you struggle to complete another repetition.
There are many ways you can strengthen your muscles, whether it's at home or in the gym. Examples of muscle-strengthening activities for most people include:
  • lifting weights
  • working with resistance bands
  • doing exercises that use your own body weight, such as push-ups and sit-ups
  • heavy gardening, such as digging and shovelling
  • yoga
Try Strength and Flex, a 5-week exercise plan for beginners to improve your strength and flexibility.
You can do activities that strengthen your muscles on the same day or on different days as your aerobic activity - whatever's best for you.
Muscle-strengthening exercises are not an aerobic activity, so you'll need to do them in addition to your 150 minutes of aerobic activity.
Some vigorous activities count as both an aerobic activity and a muscle-strengthening activity.
Examples include:
  • circuit training
  • aerobics
  • running
  • football
  • rugby
  • netball
  • hockey
For a summary on the health benefits of being more active, check out this Department of Health infographic (PDF, 500kb).
Page last reviewed: 11/07/2015
Next review due: 11/07/2017
reposted from:

crabsallover highlightskey pointscomments / links.

BMI categories may need adjusting, argue researchers

Wednesday May 11 2016
Improvements in treatments for weight-related conditions may have contributed towards the trend
There was a three-point upward shift in the 'optimal BMI' score
"Being overweight may not be as unhealthy as it was 40 years ago," BBC News reports.
New research has found a body mass index (BMI) of 27 is linked to the lowest rate of death – but someone with a BMI of 27 is currently classed as being overweight.
BMI is a score calculated by dividing your weight (usually in kilograms) by the square of your height (usually in metres and centimetres). Currently, a BMI of 25 to 29.9 is classified as being overweight.
Researchers looked at 120,528 people from Copenhagen, recruited from 1976 to 2013, and separately compared those recruited during the 1970s, 1990s and 2000s. They were followed up until they died, emigrated, or the study finished.
The BMI linked to the lowest risk of having died from any cause was 23.7 in the 1970s group, 24.6 in the 1990s group, and had further risen to 27 in the 2003-13 group.
It may be the case that the suggested upward shift in optimal BMI is the result of improvements in preventative treatments for weight-related conditions such as type 2 diabetes.
But this is just an estimate based on averages – it doesn't mean that having a "healthy" BMI is bad for you. Similarly, it shouldn't be assumed that it's now best to be in the overweight category. People often gain weight as they age, so there is the risk you could move from being overweight to obese.

Where did the story come from?

The study was carried out by researchers from Copenhagen University Hospital.
It was funded by the Danish Heart Foundation, the Danish Medical Research Council, Copenhagen County Foundation, Herlev and Gentofte Hospital, and Copenhagen University Hospital. 
The study was published in the peer-reviewed Journal of the American Medical Association (JAMA).
The study was covered by the UK media with a certain amount of glee, with the Daily Mail suggesting that the BMI system was a "blunt instrument".
It also said this study showed that, "Millions of Britons who are currently classed as overweight, actually have the optimal BMI and the lowest chance of death."
However, the study was reported on accurately, and the reports included expert views saying that people still need to keep an eye on their weight.

What kind of research was this?

This cohort study compared results from three large previous cohort studies in the same part of Denmark, starting at different times.
Researchers wanted to see if there had been a change over time in the optimal BMI score – that is, the BMI shared by people with the lowest rate of death from any cause.
While this type of study can show trends of this nature, it cannot explain why the changes happen.

What did the research involve?

Groups of adults in Copenhagen had their height and weight measured as part of three studies carried out in the city in 1976-78, then 1991-94, and the final study in 2003-13.
Researchers followed them up, then looked to see at which BMI people had the lowest chance of dying. They compared the numbers for the three studies to see if that number changed over time.
The first two studies were linked. Participants for the first study were invited back for a second round of measurements over the period from 1991-94, although younger people were recruited to add to the numbers. People in the third study had not taken part in either of the first two.
As well as weight and height, researchers checked whether people smoked, how much exercise they did, whether they'd been diagnosed with any medical conditions, including cancer or heart disease, and how much alcohol they drank.
They carried out sensitivity checks by including or excluding people with different risk factors to see whether any of them explained the overall results.
The researchers also looked at whether length of follow-up made a difference. They did this by carrying out their calculations with a much shorter follow-up period to see if the longer follow-up from the older studies distorted the results.

What were the basic results?

The average BMI at which fewest people in the studies died from any cause increased by three points over the three decades:
  • 23.7 (95% confidence interval [CI] 23.4 to 24.3) in 1976-78
  • 24.6 (95% CI 24 to 26.3) in 1991-94
  • 27 (95% CI 26.5 to 27.6) in 2003-13
The results showed a similar shift when researchers looked at just deaths from cardiovascular disease for non-smokers who had not been diagnosed with diabetes, cardiovascular disease or cancer, as well as for shorter periods of follow-up. None of the sensitivity analyses explained the trend.
In addition, researchers found the increased risk of death linked to being obese – a BMI of 30 or above – compared with a "healthy" BMI has gradually decreased to zero.
In the 1970s obese people had a 31% increased risk of death. By the 1990s it had reduced to a 13% increased risk, and by 2003-13 there was no longer a statistically significant link (adjusted hazard ratio 0.99, 95% CI 0.92 to 1.07).

How did the researchers interpret the results?

The researchers say their findings were "robust" and cannot be explained by confounding factors such as age, sex, smoking status and disease at the start of the study.
They said that, "If this finding is confirmed in other studies, it would indicate a need to revise the World Health Organization (WHO) categories presently used to define overweight."
They also said cohort studies cannot address the causes of the results, but speculated that their finding may reflect improvements in treatments for diseases affecting people with higher BMIs, such as heart disease and diabetes.
This would make it less risky to be overweight than in the 1970s, when more people died of these diseases. The reduction in smoking and increase in exercise they found could also have helped mitigate the effects of being overweight, they said.


The link between weight and health is not straightforward. We've known for years that if you plot death rates against BMI categories on a graph, you get a U-shaped curve, where people who are very underweight or very overweight are at higher risk of dying, while people in the middle have a lower risk.
This makes sense: extremes of weight are linked to illness, both as a cause or result. Many people with cancer or lung disease, for example, are underweight, which is one reason why lower BMIs are linked to higher death rates. That's why doctors talk about people having a "healthy" BMI.
What this study seems to show is that the lowest point of that U-shaped curve has shifted to the right, towards higher BMIs. But it doesn't mean that slimmer people are at a higher risk of death.
The study shows that in the period 2003-13, there was no difference between the death rates of people with a BMI of 18.5 to 24.9 (healthy) and those with a BMI of 25 to 29.9 (overweight), which were 4 per 1,000 per year for both groups.
The rate for obese people was 5 per 1,000 per year, despite this being a non-significant increased risk of death. There's certainly no need to try to put on weight if you are already at a healthy weight for your height.
The potential reasons for the shift are interesting. It may be, as the researchers suggest, that the diseases which killed more overweight people in the 1970s are now better treated and controlled, meaning that the risks of being overweight are smaller than they once were.
It's possible that the risks associated with being underweight have not decreased in the same way, which would automatically shift the "optimal" point towards overweight.
Also, despite a general increase in the population's BMI over the decades, health awareness has improved. Though the results have taken smoking status into account in the analyses, other factors, such as improvements in physical activity and alcohol moderation, could be having an influence.
However, this study has some limitations. Importantly, it was only carried out among white Danish people, which means it may not apply to other ethnic groups.
We know that some groups, such as people of south Asian origin, are more likely to have problems such as diabetes at lower BMIs than white people, so this study might not apply to everyone. And the follow-up for the most recent group studied was, on average, four years, so we don't yet know if this is a long-term trend.
The criticisms of the BMI system are not unfounded, though. BMI doesn't take into account the increased weight of muscle compared with fat – some athletes have high BMIs, despite being very fit, for example.
Waist circumference and waist-to-hip ratio can give a good indication of body "fatness". Regardless of your height or BMI, you should try to lose weight if your waist is:
  • 94cm (37in) or more for men
  • 80cm (31.5in) or more for women
You are at very high risk and should contact your GP if your waist is:
  • 102cm (40in) or more for men
  • 88cm (34in) or more for women
Read more about why waist size is important.
Analysis by Bazian. Edited by NHS ChoicesFollow NHS Choices on TwitterJoin the Healthy Evidence forum.
Analysis by Bazian
Edited by NHS Choices
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