- for each one unit rise in body mass index (BMI) the risk of experiencing heart failure increased by 17%.
- being fatter increased the risk of developing other cardiovascular diseases such as type 2 diabetes.
- The Daily Telegraph’s headline stated how “piling on as little as 4lbs can raise risk of heart attack by 17%” when in fact the 17% figure related to heart failure. These are not the same thing.
- Heart failure is a serious chronic (long term) condition whereby a damaged heart cannot pump enough blood around the body. A heart attack on the other hand is an acute medical emergency that happens when the supply of the blood to the heart is suddenly blocked.
- a one-unit increase in BMI corresponds to roughly 220,000 additional heart failure cases in Europe (113,000 additional cases in the US).
- So even a modest gain in weight (for a man who is 5'10", one BMI unit is equivalent to a seven pound or 3.2kg weight gain) can lead to extensive health costs at a population level.
Conclusion
This large study uses an interesting genetic approach (Mendelian randomisation) to suggest obesity increases the risk of heart failure and adverse changes in liver enzymes.
The combination of a very large sample, prospectively collected information, and a wide range of cardiometabolic measures lend credibility to the findings. The method the researchers used is also thought to reduce the chances of factors other than BMI influencing results, and the chance that the ‘outcome’ could be causing the ‘exposure’ (reverse causality).
The main limitation of this kind of research is that assumptions need to be made. The potentially weakest assumption is the reliability of the association between the FTO genetic variant and BMI. Although the researchers report that this link has been widely found in many other studies, they also note that the strength of the link is relatively weak – the variant is only thought to explain about 0.3% of the variation of BMI in the population.
Estimates of the effect of BMI would be more accurate if this link was stronger.
The researchers suggest that studies in the future might use more than one genetic variation to increase the strength of the link, leading to more precise estimates.
They also note that an effect of the variant on characteristics other than BMI cannot be ruled out.
Body mass index also has its limitations as a measure of fatness – you can be very muscular and have a high BMI. However, it is a widely used measure of obesity, and across the large number of people involved in the study, measuring BMI should give a reasonable measure of relative fatness.
Overall, this study provides additional evidence to suggest obesity (raised BMI) has a causal influence on a number of different cardiovascular diseases, including heart failure.
And this serves to re-emphasise the message that maintaining a healthy weight is beneficial to many aspects of health.
If you are concerned about your weight, try the free NHS Choices 12-week weight-loss guide – for an evidence-based method of working to achieve safe and sustainable weight loss.
Links to the headlines
Few extra pounds ‘could be deadly’. Daily Express, June 26 2013
Piling on as little as 4lbs can raise risk of heart attack by 17%. The Daily Telegraph, June 26 2013
Being just four pounds overweight can increase your risk of heart disease by 20%. Mail Online, June 26 2013
Links to the science
European Network for Genetic and Genomic Epidemiology (ENGAGE) consortium. The Role of Adiposity in Cardiometabolic Traits: A Mendelian Randomization Analysis. PLoS Medicine. Published online June 25 2013
