Fewer Hot Flashes Reported Among Older Heavier Women

In contradiction of recent evidence on menopausal women and hot flashes, a new study indicates that heavier women tend to have fewer hot flashes than those who are thinner. Interestingly, however, the trend is seen only among women aged 60 years and older.

Obesity has been regarded in recent years as a risk factor for hot flashes amid research indicating that heavier women tend to suffer from the menopause symptoms more commonly. These findings, which are based largely on epidemiologic studies, support a "thermoregulatory model," explain the researchers, "in which hot flashes represent heat dissipation events occurring in the context of the narrowed thermoneutral zone." Consistent with this theory is that body fat acts an insulator, increasing the frequency of hot flashes.

However, the new study, which was published online July 21 in the Journal of Clinical Endocrinology & Metabolism, suggests otherwise.

The researchers evaluated a subcohort of 52 women involved in the Study of Women's Health Across the Nation who reported hot flashes, still had their uterus and ovaries, and were not taking medications that would affect hot flashes.

Body fat, BMI, and waist circumference were most inversely associated with hot flashes among the oldest women in the sample.

Estradiol and sex hormone-binding globulin levels reduced, but did not eliminate, age-related variations in the association between body size and composition and hot flashes.

Black women reported more hot flashes; however, the association was not attributable to body size or composition: those associations were only apparent among white women, the authors wrote.

"This study provides a more nuanced understanding of the relationship between body size and hot flashes, emphasizing the important role of age," said the study's lead author, Rebecca Thurston, PhD, from the University of Pittsburgh, Pennsylvania in a press release.

"Our findings show that the benefit of higher fat levels for hot flashes is not apparent until a woman is about 60 years old."

Epidemiological studies published in the last decade or so indicate that women with higher BMIs and body fat levels are more likely to report hot flashes, but before those studies, body fat was traditionally regarded as being protective against hot flashes, and the so-called "thin hypothesis" prevailed.

Under this hypothesis, hot flashes occur because of hormonal changes including declining estrogen, and as androgens are aromatized into estrogens in body fat, women with greater levels of body fat should also have higher estrogen levels, and would logically have fewer hot flashes.

"Thinner women, lacking this extragonadal estrogen source, should have more hot flashes. [And t]his effect would be particularly relevant for older and postmenopausal women in whom extragonadal sources represent the primary source of estrogen," the researchers write.

Dr. Thurston said the new findings appear to back up that earlier theory.

"Our study showed that higher adiposity, BMI and waist circumference were associated with fewer physiologically-assessed hot flashes among older postmenopausal women with hot flashes," she noted in a press release.

"Moreover, associations were most pronounced among Caucasian women. This study underscores the importance of considering how age and race may modify the relationship between obesity and hot flashes."