These findings challenge standard thinking that thinner women, or those with less body fat, are at increased risk of hot flashes. The present findings demonstrated that women with increased abdominal adiposity, and particularly subcutaneous abdominal adiposity, were more likely to report hot flashes. Because previous research has solely considered BMI, which does not measure adipose tissue, these findings provide stronger evidence against the thin hypothesis. Together with findings with BMI,1,11,12
they suggest the potential importance of considering obesity, and subcutaneous adiposity in particular, as a risk factor for hot flashes.
The overall association between abdominal adiposity and hot flashes was positive, consistent with thermoregulatory models of hot flashes. We also evaluated the contribution of reproductive hormones, recognizing that these concentrations reflect the contribution of estrogen from the ovary rather than aromatization of androstenedione from adipose tissue, limiting conclusions about peripheral production. However, we are operating under the assumption that these measures are a fair approximation of the total estrogen contribution because 70% of women are not postmenopausal and E2 is a more potent estrogen than E1. Although FSH and FEI were associated with both adiposity and hot flashes, adjusting for these hormones failed to attenuate the association between abdominal adiposity and hot flashes. Further investigation with more complete hormonal assessment is warranted. However, these findings suggest that although abdominal adipose tissue may have both thermoregulatory and endocrine properties, the insulating properties of adipose tissue may be more strongly related to hot flashes.
Thermoregulatory models of hot flashes conceptualize hot flashes as attempts to dissipate heat in the context of a narrowed thermoneutral zone.13
The observation that positive associations between abdominal adiposity and hot flashes were most pronounced for subcutaneous fat is consistent with these models. The potent insulating properties of subcutaneous fat are well known, with evidence indicating that it insulates three times as well as muscle.14
Moreover, in these investigations, the amount of heat dissipated is inversely related to subcutaneous adipose tissue thickness.15
Thus, increased subcutaneous adiposity would prevent the heat-dissipating action of hot flashes and require more hot flashes to achieve requisite heat loss.13
The adiposity values obtained here are consistent with what would be expected of a multiethnic community sample of women in this age range.21-26
However, it is notable that large community-based studies that include CT-assessed abdominal adiposity in a sample of African American and white midlife women are few. In the present investigation, a differential distribution of adiposity was observed between racial/ethnic groups, with proportionately lower contribution of visceral to total adiposity levels among African American relative to white women. This finding is consistent with previous investigations.26-28
There is considerable interest in behavioral interventions for hot flashes. For example, aerobic exercise has been suggested as one initial approach to managing hot flashes.29
However, associations between exercise and hot flashes have been highly inconsistent,30-32
and randomized trials are few. In light of the present findings, interventions focused on fat reduction for the management of hot flashes may deserve further investigation. These interventions may be particularly important during a period of life characterized by progressive increases in adiposity,33
including abdominal adiposity.34
The present findings should be interpreted in the context of several limitations. First, SWAN Heart participants underwent a single annual blood draw, which, given the hormonal fluctuations during perimenopause, is a less optimal measure than daily hormone assessments. This method may have increased error and biased findings to the null. However, significant associations were observed for hormonal measures in relation to both adiposity and hot flashes. Second, this study included assessment of abdominal adiposity rather than total adiposity. The relationship between total adiposity and hot flashes cannot be determined from this study. Third, this study was a cross-sectional analysis, limiting conclusions about the causal nature of associations and how the observed associations may change over time, including later in postmenopause. Fourth, not unlike most epidemiologic investigations, hot flashes were measured via a brief self-report instrument that yields limited information about hot flashes. Compared with physiologic measures, reported hot flashes may be influenced by factors such as mood and affect.35
However, controlling for anxious symptoms, strongly related to hot flashes,1,16
did not reduce these associations. Finally, this study included African American and white women. Whether these findings extend to other groups is unknown.