October 5, 2009
More Reasons Not To Get Fat
By Michael D. Shaw
Obesity has long been associated with an increased risk of morbidity, including such conditions as diabetes, heart disease, arthritis, and certain types of cancer. Many studies have looked at the body mass index (BMI) in relation to various health effects. The BMI is calculated by dividing your weight in kilograms by the square of your height in meters. A convenient web-based calculator—allowing you to input these values in either metric or conventional units—is provided by the National Institutes of Health.
BMI is a good indicator of total body fat, given two principal limitations…
- It may overestimate body fat in athletes and others who have a muscular build
- It may underestimate body fat in older persons and others who have lost muscle mass
Another parameter of interest is visceral or abdominal fat, which translates, of course, into a larger waist size. A study published last year in the American Journal of Epidemiology entitled “Waist Circumference and Mortality,” established the disturbing finding that even people with normal BMIs were at a 20 percent increased risk of mortality if their waist circumference were “large.” [Defined in this study as ≥102 cm (40 in) for men and ≥88 cm (35 in) for women.]
A team of researchers led by Qi Sun and Professor Francine Grodstein, both affiliated with the Harvard School of Public Health, were interested in how adiposity (i.e. being fat) at mid-life affects overall health and well-being among those who survive to older ages. The study, entitled “Adiposity and weight change in mid-life in relation to healthy survival after age 70 in women: prospective cohort study,” appeared in the online version of the British Medical Journal on September 30, 2009.
The authors examined data derived from the Nurses’ Health Study, originally started in 1976 with a cohort of 121,700 registered nurses, aged 30-55, living in one of 11 US states. The study population included 17,065 female participants who had survived until at least age 70. BMI and weight gain were measured over time, beginning at mid-life (age 50). Waist circumference was also considered. Factors such as socioeconomic status, lifestyle, smoking and diet were controlled for statistically.
“Healthy survivors” were those women (1,686 or 9.9%) who lived until at least the age of 70, and reported being free of major chronic diseases, had good cognitive and physical functions, and had good mental health. “Usual survivors” were those remaining (15,379) who also survived at least until age 70.
Among the “usual survivors,” 3.3% had chronic diseases but no other health limitations; 59.5% had cognitive, physical or mental health limitations but no diagnosed major diseases; and 37.1% suffered from both chronic diseases and cognitive, physical, and mental health limitations. The most common chronic diseases were cancer, coronary heart disease, and diabetes.
As to the obesity connection, here are some key findings…
- Every one unit increase of BMI was associated with a 12% reduction of the odds of healthy survival
- Obese women (BMI ≥30) had 79% lower odds of healthy survival compared with lean women (BMI=18.5-22.9)
- Women who were overweight (BMI ≥25) at age 18 and gained more than 22 pounds between age 18 and 50, had the worst odds of healthy survival
Waist circumference (adjusted for BMI) was associated with reduced odds of healthy survival, on a proportionate basis from 71-88 cm (28-35 in), with 73% lower odds of healthy survival at ≥88 cm (35 in).
I’ll let the lead researchers get in the last word.
“Since body weight is a modifiable factor, the good news is that healthy aging is not purely the consequence of good genes or other factors that one cannot change. If women maintain a healthy weight as adults, they may increase their odds of enjoying a healthy life in their later years,” said Qi Sun.
“An important aspect of this study is the broad focus on many aspects of health, and not just on whether people get a single disease. Our finding that being overweight at mid-life affects so many aspects of health simultaneously really emphasizes the harms of being overweight,” said Prof. Grodstein.