Flashes and body composition and age, oh my! What’s the relationship?

Posted by Liz on Jul 22, 2011 in aging, hot flash | 0 comments

For some time now, experts have made the connection between body mass index (BM() and hot flashes during menopause, theorizing that body fat offer protection against hot flashes since androgen hormones are actually converted into estrogens in body fat. On  the flip side? Women with lower BMI should have more frequent hot flashes. However, this hypothesis — formally known as the “thin hypothesis” – has recently been questioned, especially among researchers whose studies have shown the opposite: that a higher BMI leads to more hot flashes because the fat acts to insulate the body and prevent heat dissipation. In the middle of this argument are women, overweight, underweight, normal weight, who may have an opportunity to prevent hot flashes before they worsen or at least ameliorate them.

To more thoroughly tease out the underlying causes of hot flashes as they relate to body composition, researchers evaluated a subset of 52 women participating in the larger Study of Women’s Health Across the Nation (SWAN, an ongoing trial at seven sites across US that are examining women’s health in middle age). These women were African-American or non-Hispanic Caucasians between the ages of 54 and 63, mostly overweight, in menopause and reported experiencing hot flashes or night sweats. None were taking hormones or antidepressants, and still had their uterus.

In the study, published online in the Journal of Clinical Endocrinology and Metabolism, broad measures of central abdominal fat/total percentage of body fat, BMI and waist circumference and blood hormones were taken. Over two, 48-hour periods, participants also wore a monitor to evaluate the frequency and severity of hot flashes and were asked to both complete electronic diaries and press buttons on their monitors that would notate when they were experiencing symptoms.

The result? A higher percentage of body fat, BMI and waist circumference were associated with a reduction in the frequency of hot flashes only in women who were 59 or older. Moreover, this association was restricted to Caucasian women in the study compared to their Black peers.  However, in so far as the interaction between estrogen levels (and sex hormone-binding globulin) and body composition, researchers found that higher levels reduced but did not fully eliminate the distinctions in hot flashes and age.

So, why the differences compared to other studies? Others have looked as self-reported hot flashes via questionnaires while this one actually took physiological measures of hot flashes via the monitors that the women were wearing. The researchers also looked specifically at the link between size, weight and proportions of the women and hot flashes rather than risk factors of any or no hot flashes.

Importantly, data are starting to emerge that show how BMI/adipose fat and the relationship to reproductive hormones varies by age and menopause status, with higher estrogen levels related to older, menopausal women and lower to younger women. What’s more, while body fat may act to produce estrogen in older women to play a role in regulating body heat and dissipation, it seems to play a different role in younger, overweight women, predisposing them to hot flashes. Finally, wellbeing also appears to play a role in symptoms: in this case, women who were anxious reported more hot flashes and hot flashes tended to increase anxiety.

Should you care?

Although the sample size is small, the is first time that researchers have considered how age and race affect the way that obesity may affect hot flash frequency. It’s worthwhile filing it under “useful information,” especially when it comes to perimenopause and preparing to deal with full blown symptoms as you enter menopause.

A special thanks to my pal Ivan Oransky, executive editor of Reuters Health and author of Retraction Watch  for giving me a heads up on this study. Thanks Ivan!