OBESE WOMEN ARE FIVE TIMES MORE LIKELY TO DIE FROM CHD

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June 14 - 20, 2004
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The relationship between body weight and mortality is the subject of intense debate. In this study, the association between body mass index (BMI) and overall mortality, and mortality from specific causes was examined in women. Body weight was directly related to all-cause mortality in middle-aged women, after smoking and pre-existing illness were taken into account. The study found that the leanest women had the lowest mortality, and even women of average weight had higher mortality.

KEY RESULTS

There was a 'J'-shaped relationship between BMI and overall mortality when women who smoked were included.

Women with the lowest mortality had a BMI between 19.0 and 26.9 (measured in kg/m2).

Of the deaths of obese women (BMI>29.0), 53% could be attributed to their obesity.

When former or current smokers were excluded from the analysis, the relationship between mortality and BMI became more direct.

Women with the lowest mortality had a BMI of < 22.

The most direct association between BMI and mortality occurred when both cigarette smoking and disease-related weight loss were accounted for.

These optimal analyses included only women who had never smoked and who had stable weight in the previous 4 years (i.e. no weight changes of 4 kg or more).

The leanest women (those with a BMI < 19) had the lowest mortality. Mortality among obese women (those with a BMI of > 29) was over twice that for the leanest women.

The apparent excess risks associated with leanness were found to be artefacts in this study, and were eliminated after cigarette smoking and subclinical disease were accounted for.

Obese women were four times more likely to die due to cardiovascular disease and five times more likely to die due to coronary heart disease (CHD) than the leanest women.

Reported hypertension, diabetes and raised serum cholesterol levels were two to six times more prevalent among women in the heavier categories.

Self-reported dietary fat and cholesterol intake varied very little in relation to BMI category.

Mortality due to cancer in obese women was twice that in the leanest group of women.

 

 

This increased prevalence of death due to cancer was predominantly due to colon, breast and endometrial cancers.

There was a trend towards higher mortality due to coronary heart disease, other cardiovascular diseases and cancer, even among women of average weight and those who were mildly overweight.

Never-smoking women with a BMI of 27.0-28.9 had a relative risk of death due to cardiovascular disease up to 1.8 times greater than the leanest group of women (BMI < 19) .

Even women with a BMI of 22.0-24.9 had a higher relative risk of death due to cardiovascular disease than the leanest group of women.

The relative risk of death due to cancer was higher in the group whose BMI was 19.0-21.9 than in the leanest group of women.

A weight gain of 10 kg or more since 18 years of age was associated with an increased mortality in middle adulthood.

Women who had gained 10-19 kg since 18 years of age had a relative risk of overall mortality 1.2 times that of women whose weight had remained stable (defined as no weight fluctuations of 4 kg or more).

Women who had gained 20 kg or more since 18 years of age had a relative risk of overall mortality 1.6 times that of women whose weight had remained stable. The waist-to-hip ratio was a strong predictor of death due to CHD.

BMI was a stronger predictor of overall mortality than the self-reported waist-to- hip ratio, however, women whose waist-to-hip ratio was in the highest fifth of the cohort had a relative risk of death due to CHD over eight times higher than that of the lowest fifth.

METHODS

This 16-year study started in 1976 and followed 115195 female registered nurses aged 30-55 years. Data were collected by questionnaires, and were controlled to eliminate bias due to pre-existing diseases. Participants completed questionnaires every two years, supplying age, current weight and height, current and past cigarette smoking, other risk factors, medical history and newly diagnosed major illnesses. In 1980, data on food frequency, physical activity, and participants' weight at 18 years of age were also collected.

Overall mortality was the primary end-point and, where possible, the cause of death was determined. The mortality rate for a specific category of BMI was calculated by dividing the number of deaths by the cumulated number of person years of follow-up. Participants were grouped into seven categories of BMI as follows: < 19.0,19.0-219,220-249, 25.0-26.9,27.0-28.9,29.0-31.9 and > 32. The relative risk for a specific BMI category was used as a measure of the strength of association. This was calculated by dividing the mortality rate by the rate for the leanest BMI category ( < 19) . The proportion of deaths attributable to adiposity was calculated by dividing the difference between the mortality rate of a specific category and the rate for the leanest category by the rate for the specific category.