Hot Flashes and Exercise
Hot Flashes and Exercise
By Felise B. Milan, MD Dr. Milan is Associate Professor of Clinical Medicine, Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, NY. Dr. Milan reports no consultant, stockholder, speaker's bureau, research, or other financial relationships with companies having ties to this field of study.
The most prevalent symptom associated with menopause, hot flashes often have been attributed to causing significant sleep disturbances.1 Frequent awakenings at night can lead to chronic fatigue, irritability, mood disorders, and changes in memory or attention span.1-3 Although vasomotor symptoms can be treated effectively with estrogen replacement therapy, many women now seek an alternative therapeutic option due to the multiple risks associated with estrogen replacement therapy.
Epidemiology of Hot Flashes: The Scope of the Problem
The terms hot flash, hot flush, and vasomotor symptoms often are used to describe the phenomenon of recurrent, transient episodes of flushing, perspiration, and a sensation of warmth on the upper body and face. Hot flashes that occur during sleep and are accompanied by perspiration are termed night sweats. The North American Menopause Society (NAMS) defines vasomotor symptoms as a global term that includes both hot flashes and night sweats. NAMS prefers the term hot flash rather than hot flush.4
The symptoms of vasomotor instability are considered one of the hallmark signs of perimenopause and menopause. Women experience vasomotor instability manifested by episodes of intense heat and sweating followed by a cold and clammy sensation. These episodes, or hot flashes, may last for seconds or minutes with an average of four minutes.5
The majority of women who experience hot flashes report them on average two years before the total cessation of menses.1 In one prospective study, 31% of women experienced some hot flashes before noting any irregularity in their menstrual cycle.6 The incidence of hot flashes reaches its highest incidence during the first two years postmenopause.4 Although most women experience hot flashes for six months to two years, some can have them for 10 years or more.1,7 The frequency of hot flashes varies widely among effected women (monthly to hourly). Hot flash frequency typically peaks in the early evening, about three hours after the peak in core body temperature.8
Factors Associated with Hot Flashes
The number of women who experience these symptoms varies widely with regard to race and ethnicity. Women in Western countries have approximately an 80% incidence of hot flashes; Asian women have an incidence of 20% if they live in China9 and 10% if they live in Hong Kong.10 The lower incidence of vasomotor symptoms in Asian women has been reported widely.11-13 It has been hypothesized that the differences may be attributed to soy-rich diets.9,14 The Study of Women's Health Across the Nation (SWAN), a multi-ethnic, multisite study of 16,065 U.S. women ages 40-55 years found that even after controlling for age, education, health, and economic status, African American women reported significantly more vasomotor symptoms (45.6%) than did Hispanics (35.4%), Caucasians (31.2%), or Asians (18%).15,16 The higher incidence of hot flashes in African American women has not been widely replicated or explained. Other factors that have been associated with an increased incidence of hot flashes are smoking,15,17,18 fewer year of education,16,19,20 a history of premenstrual complaints,21 and lower socioeconomic status.15
The relationship between body mass index (BMI) and incidence of vasomotor symptoms is less clear. Although it previously was believed that hot flash risk was inversely related to BMI secondary to the production of estrogens in adipose tissue, many studies have found just the opposite. In a cross-sectional study of 1,087 women ages 40-60, Whiteman found that the odds of reporting hot flashes was more than two times greater in those with BMI > 30 kg/m2 compared to those with BMI < 24.9 kg/m2 (adjusted odds ratio [OR] = 2.11).17 In the 40-50 age group, that risk was even greater (OR = 2.3). In the SWAN study, women with a BMI > 32 kg/m2 were significantly more likely to report hot flashes than women with a BMI < 19 kg/m2 (43.8% vs. 30.6%).15
Pathophysiology of Hot Flashes
To best understand the relationship that has been found between physical activity, exercise, and the incidence of hot flashes, it is useful to consider some of the theories of the pathophysiology of vasomotor symptoms in menopausal women. Vasomotor symptoms are attributed to the withdrawal of estrogen as ovarian function is intermittently diminished during the perimenopausal transition. It is the relative decrease in estrogen and not the absolute estrogen level that will predict the occurrence of hot flashes.22-24 It has been widely hypothesized that this decrease in estrogen levels causes the dysfunction of central thermoregulatory centers in the hypothalamus that is the primary cause of vasomotor instability of menopause.4,25
There are data to suggest that women with hot flashes may have a thermoregulatory zone that is shifted downward and narrower than women who do not report hot flashes,26 and that small changes in core body temperature occur 15 minutes before triggering hot flashes in up to 60% of hot flashes.8 These changes are thought to be mediated primarily by central norepinephrine levels24,26,27 and also may be effected by central serotonin levels. Beta-endorphin levels also decrease with falling estrogen levels and are thought to play a role in thermoregulation.28 Norepinehrine production and release in the thermoregulatory nucleus are inhibited by endorphins and catecholestrogen, a metabolic byproduct of estrogen metabolism.29 Estrogen withdrawal also is associated with a decrease in serotonin levels and up-regulation of serotonin receptors in the hypothalamus.30
A model of hot flash pathogenesis by Shanafelt proposes that estrogen withdrawal leads to a decrease in endorphin and catecholestrogen levels, resulting in increased hypothalamic norepinephrine and serotonin release.25 This lowers the set-point in the thermoregulatory nucleus, allowing heat loss mechanisms to be triggered by subtle changes in core body temperature. Women who exercise regularly have higher central endorphin levels.31,32 Therefore, the role of exercise either can decrease the incidence of hot flashes by increasing beta-endorphin levels or serve as a trigger of hot flashes by acutely increasing core body temperature. The other obvious connection between physical activity and hot flashes is BMI. Women who exercise regularly have a lower BMI, which is associated with a lower incidence of hot flashes. The multiple possible effects of exercise on the pathophysiology of hot flashes may explain the great variability of findings in the literature looking at this relationship.
Data on Exercise and Hot Flashes
The studies looking for a relationship between physical activity or exercise and vasomotor symptoms in menopausal women has not produced clear answers. The first of three studies done in Sweden was a comparative cohort study where questionnaires about menopausal symptoms were sent to 142 women (ages 50-58) who were active members of a local gym and all women (n = 1,246; control) aged 52-54 in the same municipality.33 Women from the community sample experiencing natural menopause and not on hormone replacement therapy were compared to the gym members; the researchers found that moderate flushes and sweating were half as common among the women belonging to the gym (21.5%) as in the control group (43.8%). However, since level of physical activity was not assessed in the control group, no conclusion can be made about the relationship between exercise and hot flashes from this study.
In another Swedish study, researchers sent questionnaires on menopausal symptoms (present and past) and physical exercise to all women (n = 1,323) ages 55-56 in the same community as the above study.28 Of the 793 women who had experienced a natural menopause, the relative risk of severe hot flashes in women exercising at least two hours per week compared with non-exercising women was 0.26 (95% confidence interval [CI] = 0.10-0.71). However, the rate of hormone replacement therapy use was significantly higher in the women who exercised, and the distinction between past and present experience with hot flashes is not clearly reported. It appears that past experience with hot flashes was compared with current level of exercise. These two studies frequently are cited as evidence that exercise decreases hot flashes.
A large population-based study, Women's Health in the Lund Area, interviewed middle-aged women (ages 50-64 years, n = 6,917) about many aspects of their health and symptoms.20 In a logistic regression analysis, a lower intensity of hot flashes was associated with vigorous exercise. However, in the multiple regression models, exercise was not found to be an independent variable.
In a cross-sectional study done in Australia in which 2,000 women between 45-55 years were interviewed, researchers found no relationship between physical activity and a variety of menopausal symptoms.34 In another community-based study in Australia, 220 women who were premenopausal, perimenopausal, or postmenopausal were interviewed about level of exercise and menopausal symptoms and completed two instruments to assess mood and well-being.35 The scores of the women who reported exercising regularly reflected more positive mood and physical well-being, but this was independent of menopausal status. However, most of the women in this cohort who exercised did low-to-moderate levels of exercise; vigorous exercise is required to elevate endorphin levels.
The few interventional studies on exercise and vasomotor symptoms have been very small and flawed. A small study in Japan divided 35 women into two groups.36 One group (n = 15) received information about menopausal symptoms and participated in a one-hour aerobics class three times a week for 12 weeks and the other group (n = 20) just received the information and was asked not to exercise for the duration of the study. The exercise group improved significantly on the Japanese version of the Kupperman Index but did not differ from the education-only group on vasomotor symptoms score. In addition to the groups not being randomized, the control group had a higher Kupperman score (18.2) than the intervention group (15.8) at baseline.
An interventional study done in Sweden randomized 75 postmenopausal sedentary women with vasomotor symptoms to exercise three times per week (n = 15), oral estradiol therapy (n = 15), two different modes of acupuncture (n = 15 each), or applied relaxation (n = 15) for 12 weeks.37 Women reported both the frequency and severity (on a visual analog scale) of their hot flashes. Of the 10 women who completed the 12 weeks of exercise, five had no change in hot flashes and five had a 28% decrease at 12 weeks. These latter five women continued to exercise and had a significant decrease in both frequency and severity of hot flashes at 24 weeks (75%) and at 36 weeks (72%).
In Seattle, a group of overweight (average BMI = 31 kg/m2) postmenopausal women not on hormone replacement therapy (n = 173) were randomized to either a moderate intensity exercise group (45 min, five times per week) or stretching control for one year.38 Only six women dropped out of the exercise group and an intention-to-treat analysis was used. Overall, there was no significant difference in reports of menopausal symptoms between the two groups. However, the cohort was not chosen for presence of vasomotor symptoms, and only 15% of the intervention group and 19% of the controls reported any hot flashes at baseline. In the small group of women with moderate-to-severe vasomotor symptoms, there was a significant trend in the exercise group toward an increase in hot flashes (P = 0.02). Since all the women in this study were overweight, it is difficult to know whether these findings are applicable to normal weight women.
Summary and Recommendations
The physical and psychological benefits of exercise for perimenopausal and postmenopausal women include substantial reductions in the incidence of cardiovascular events,39 a reduced risk of breast cancer,40,41 a increase in bone mineral density,5,42 and a significantly reduced risk of hip fracture.25 Exercise obviously lowers the percentage of body fat and BMI and greatly improves many aspects of quality of life.1 The exact mechanism by which exercise may modulate hot flashes remains unknown and there are not adequate data to clearly show that regular exercise reduces the incidence or severity of vasomotor symptoms during menopause. However, it does seem likely that in normal weight women, regular moderately vigorous exercise may be beneficial for hot flashes. Even if a woman does not experience the benefits of reduced hot flashes, the other known benefits of regular exercise for postmenopausal women are so profound that women should be encouraged to take up an exercise program.
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Milan F. Hot flashes and exercise. Altern Ther Women's Health 2005;7(12):89-93.Subscribe Now for Access
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