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Sunday, 8 August 2010

Which BMI gives the lowest risk of death? Why the pot belly is a killer.

source: New Scientist, 12 November 2008
An expanding waistline could double your risk of death
(Image: Wikimedia commons)




Updated: 8/8/10.
Crabsallover Notes: Among male participants who had never smoked, the risk of death was lowest:
  1. at a BMI of 24.5 (supplementary Figure 2)
  2. 85cm waist circumference (supplementary Figure 3)
  3. 0.88 waist to hip ratio.(supplimentary Figure 3).




22:00 12 November 2008 by David Robson
Having trouble slipping into those jeans? That expanding belly could as much as double your risk of premature death, even if your weight is considered healthy.
While obesity is a well-known predictor of diabetes, heart disease and some kinds of cancer, a major new study shows that a paunch poses its own particular risks, independently of fat stored elsewhere in the body. This suggests that the size of someone's waistline as well as their body mass index should be taken into account in assessing their health.
The team behind the study, including researchers from Imperial College London and the German Institute of Human Nutrition in Potsdam-Rehbr├╝cke, followed the health of 359,387 people from nine European countries over roughly 10 years. They wanted to examine a link between waistline and health that had been found in earlier smaller-scale studies. Previous animal studies had also suggested that visceral fat around the belly has more negative effects on health than fat in the thighs of the hind legs.
After controlling for factors such as overall obesity, the team found that the risk of premature death among subjects with a waist exceeding 120cm (47.2in) for men and 100cm (39.4in) for women was twice that for those whose waists were under 80cm (31.5in) for men and 65cm (25.6in) for women.
For a given BMI, a 5cm increase in waistline increased the risk of premature death by 17% in men and 13% in women.

A simple predictor of risk

"There aren't many simple individual characteristics that can increase a person's risk of premature death to this extent, independently from smoking and drinking," says Elio Riboli from Imperial College London, who was part of the team.
The ratio of waist size to hip measurement also appears to be an important predictor of the risk of premature death. Most waist-to-hip ratios for men ranged from 0.78 and 1.10 for men, and for a given ratio, an increase by 0.1 increased the chance of premature death by a whopping 34%. Most female waist-to-hip ratios were in the 0.66-0.98 range, and (again for a given ratio) an increase of 0.1 resulted in a 24% jump in risk.
The team speculate that fatty deposits around the waist could secrete elevated levels of hormones and other signalling proteins called cytokines that lead to chronic illnesses like heart disease and cancer.
"Abdominal fat is not a mere energy depot, but it also releases messenger substances that can contribute to the development of chronic diseases. This may be the reason for the link,"
says Tobias Pischon of the German Institute of Human Nutrition.

Review by Crabsallover
Journal reference: New England Journal of Medicine, vol 359, p 2105 (Full Text)
Table 1. Relative Risk of Death According to BMI among Men and Women in the European Prospective Investigation into Cancer and Nutrition.
Current guidelines with respect to obesity recommend the measurement of waist circumference in persons with a BMI between 25.0 and 34.9 and propose cutoff points for waist circumference of 102 cm in men and 88 cm in women (and cutoff points for waist-to-hip ratio of 1.0 in men and 0.85 in women) to define abdominal obesity and to identify persons at risk for disease.2 However, less is known about the association of waist circumference or waist-to-hip ratio with the risk of death.

There was a significant nonlinear association of BMI with the risk of death, with the lowest risks at a BMI of 25.3 among men and 24.3 among women
and increased risks in the lower and upper BMI categories (Table 1 and Figure 1).
Figure 1. Adjusted Relative Risk of Death among Men and Women in the European Prospective Investigation into Cancer and Nutrition, According to BMI, Waist Circumference, and Waist-to-Hip Ratio.
The relative risk of death in association with body-mass index (BMI, the weight in kilograms divided by the square of the height in meters), waist circumference, and waist-to-hip ratio is shown in Panel A for men and in Panel B for women. Solid lines indicate relative risks, and dashed lines indicate 95% confidence intervals. The relative risks are plotted on a logarithmic scale.







Table 2. Relative Risk of Death According to Quintiles of Waist Circumference among Men and Women.
According to the Crude measure
the optimum waist measurement is 86-<91.5cm>
After further adjustment for BMI, waist circumference and waist-to-hip ratio showed a strong positive association with the risk of death (Table 2 and Figure 2, and Table 3 in the Supplementary Appendix). For a given BMI in men and women, a waist circumference that was 5 cm larger was associated with a risk of death that was increased by a factor of 1.17 among men and by a factor of 1.13 among women, and a waist-to-hip ratio that was 0.1 unit higher was associated with a risk that was increased by a factor of 1.34 among men and by a factor of 1.24 among women. In models that included waist circumference or waist-to-hip ratio, BMI remained significantly associated with the risk of death. Hip circumference was not significantly associated with the risk of death after adjustment for BMI.

Figure 2. Adjusted Relative Risk of Death among Men and Women, According to Waist Circumference and Waist-to-Hip Ratio after Adjustment for BMI.
The relative risk of death in association with waist circumference and waist-to-hip ratio, after adjustment for BMI, is shown in Panel A for men and in Panel B for women. Solid lines indicate relative risks, and dashed lines indicate 95% confidence intervals. The relative risks are plotted on a logarithmic scale.
Subgroup Analyses

Among participants who had never smoked, the risk of death was lowest at a BMI of 24.5 for men and 23.9 for women

Amongst Men who have never smoked (Supplimentary Figure 3) the lowest risk of death was with 85cm waist circumference / 0.88 waist to hip ratio.
(Figure 2 and Figure 3 in the Supplementary Appendix).

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