Physical Activity in Women’s Health
- • Regular physical activity conveys multiple benefits for women throughout the lifespan.
- • Regular physical activity lowers the risk of various chronic diseases including coronary heart disease, diabetes, obesity and weight gain, and certain cancers.
- • Regular physical activity is important for brain health and cognition.
- • Regular physical activity plays important roles for both pregnancy and postpartum including decreased risk of excessive weight gain and improved fitness and emotional well-being.
Regular physical activity can play multiple important roles in women’s health (1-3). These benefits range from reducing the likelihood of dying from multiple causes to reducing specific risk factors for coronary heart disease (CHD), obesity, diabetes (T2DM), and certain cancers. Cognition affect and other aspects of brain health can also be improved in women with regular physical activity throughout the lifespan.
Regular physical activity can also play important roles both during pregnancy and post-partum as well as menopause (4). In addition, physical activity can play an important role in breast health, bone health, and osteoporosis as well as the preservation of healthy body composition (1-3).
The purpose of the current chapter is to summarize the various ways the physical activity can play important roles in preserving or improving the health of women. Different benefits come from aerobic exercise compared to resistance training, however, both are important.
Multiple organizations including the American Heart Association (AHA) (5), Physical Activity Guidelines for Americans 2008 (6) and 2018 (3), and the American College of Sports Medicine (ACSM) (7) have all issued guidelines and recommendations for regular exercise. Typically these guidelines involve 30 minutes of moderate intensity physical activity on most days or perhaps vigorous intensity physical activity of at least 25 minutes two or three days a week.
Unfortunately, only approximately 28% of women exercise enough to meet these basic guidelines and 41% engage in no physical activity at all (8). Aerobic activity has been the focus of most research on health benefits for women. Resistance exercise, however, may also confer health benefits particularly in the area of bone density and musculoskeletal function. Yet only 17.5% of women engage in strength training at least twice a week which is recommended by the current guidelines (9-11).
While most of the recommendations involve 30 minutes of moderate intensity physical activity on most days and two sessions of resistance strength training per week, even much smaller levels of regular physical activity can substantially reduce the risk of various chronic illnesses. Moreover, there is a dose/response relationship such that individuals who exercise at higher levels than the current recommendations may derive additional benefits (3). All these issues will also be explored in this chapter.
While this chapter will focus on largely on aerobic physical activity, other risk factors that have to do with lifestyle decisions may also significantly impact on the likelihood of developing various chronic diseases including CHD and Type 2 Diabetes (T2DM). For example, the Nurses’ Health Trial demonstrated that 84% of all CHD and 91% of diabetes could be eliminated if women followed five simple practices including regular physical activity (30 minutes on most days), maintain a proper healthy weight (BMI <25 kg/m2), follow sound nutritional practices (e.g. more fruits and vegetables, whole grains and several fish meals a week), do not smoke cigarettes, and consume only moderate amounts of alcohol (1 alcohol beverage per day) (2).
Multiple prospective and cohort studies show inverse associations between physical activity and all-cause mortality. The Physical Guidelines for Americans 2008 estimated a 30% decrease in risk of all-cause mortality when comparing the least to most active individuals (6). Further risk decreases were noted in the 2018 Physical Activity Guidelines for Americans Scientific Report (3). Even individuals who exercised only 30 minutes per week achieved a 20% decrease in risk of all-cause mortality, while individuals who exercised 1.5 hours per week had a further 30% reduction in all-cause mortality. Recent evidence utilizing accelerometers showed that there was a reduction in risk factors for heart disease of 60-70% in women when comparing the highest to the lowest levels of physical activity (12).
In a meta-analysis of 22 large cohort studies involving 643,000 women and 335,000 men those who performed 2.5 hours per week of moderate intensity physical activity (equivalent of 30 minutes a day, 5 days a week) experienced a 19% reduction in all-cause mortality, while those who performed 30 minutes of moderate activity on a daily basis reduced their mortality risk by 24% (13).
According to the National Institute of Health (NIH), American Association of Retired Persons (AARP) Diet and Health Study which involved 253,000 women, those who engaged in moderate intensity physical activity 3 hours or greater experienced a 27% decrease in risk of mortality compared to no physical activity (14). Those who engaged in vigorous activity for 20 minutes greater than 3 times a week achieved a 32% reduction in risk (15).
In addition, a number of studies have shown that time spent in sedentary living represents an independent risk factor for all-cause mortality. The American Cancer Society’s Cancer Prevention Study II (CPS-II) showed that individuals who were involved in sitting greater than six hours per day experienced a 37% increase in mortality (16). Those who were involved in sedentary occupations, yet managed to maintain recommended levels of physical activity were able to substantially ameliorate this risk (17).
PHYSICAL ACTIVITY AND CORONARY HEART DISEASE (CHD)
Physical activity plays a substantial role in reducing the risk of CHD in women (16). This is particularly important since CHD is the leading cause of death in women by age 65. Since women tend to get serious manifestations of heart disease such as myocardial infarction (MI) and sudden cardiac death at a later age than men. women who have developed CHD have a significantly worse prognosis than men. Unfortunately, in a national survey of physician awareness of CHD prevention guidelines, less than one in five physicians knew that more women than men die each year because of CHD (1).
Multiple studies have shown that 30 minutes per day of moderate intensity physical activity substantially lowers the risk of CHD in women. In the Women’s Health Initiative Observational Study (18), walking briskly for at least 2.4 hours per week (approximately 30 minutes five times per week) was associated with a 30% reduction in cardiovascular events over a 3.2 year follow up. In an 8 year follow up study of 72,000 healthy middle aged female nurses three hours of brisk walking or 1.5 hours of vigorous exercise per week resulted in a 30-40% lower risk of MI compared to sedentary individuals (19). Other studies have shown similar benefits.
It used to be thought that physical activity needed to be at least ten minutes in duration per session to yield benefits. The most recent data, however, summarized in the PAG A 2018 Scientific Report showed that any level of increased physical activity will result in reduced risk of CHD (20). In addition to aerobic physical activity, women who train with weights greater than 30 minutes per week are 23% less likely to develop CHD over an 8 year follow up. yet only 17.5% women engage in strength training at this level (21).
PHYSICAL ACTIVITY AND TYPE 2 DIABETES
Many studies have demonstrated that regular physical activity lowers the risk of diabetes in w'omen. In the Women’s Health Study participants who reported walking 2-3 hours per week were 34% less likely to develop T2DM over a 7 year follow'-up compared to those who reported not walking (22). In a study of 4,369 middle aged Finnish women and men, followed for 9.4 years, individuals who walked or cycled to wwk for at least 30 minutes per day experienced a 36% reduction in the risk of T2DM compared to peers who did not engage in these activities (23).
It should be noted that physical inactivity and obesity independently contribute to the development of both CHD and T2DM in initially healthy women. Furthermore, regular physical activity with or without concomitant weight loss can prevent or postpone diabetes onset as reported in a variety of intervention studies.
It is thought that regular physical activity slows the initiation and progression of diabetes through a variety of favorable effects including lower body weight, increased insulin sensitivity, improved glycemic control, lower blood pressure, improved lipid profile, enhanced endothelial function, improved hemostasis, and more effective inflammatory defense systems (24). One randomized controlled study showed that a combination of aerobic and resistance exercise lowered the risk of diabetes more than either modality alone (24). Both the Diabetes Prevention Program (DPP) (25) and the Finnish Diabetes Study (23) showed significant decreases in the likelihood of developing diabetes in individuals with impaired fasting glucose who were involved in physical activity 150 minutes per week and achieved a 5-7% loss of body weight.
More detail about the relationship between physical activity and diabetes in both men and women may be found in Chapter 5.
The United States and much of the developed world are in the midst of pandemics of overweight and obesity (26). Regular physical activity is an important adjunct to weight loss programs and very important to lower the risk of weight gain in healthy weight women. While physical activity alone yields only modest benefit in terms of initial weight loss (on the order of 2-3%), regular physical activity is very important for the long-term maintenance of weight loss (27). Numerous studies have documented that both caloric restriction and physical activity play important roles in long-term maintenance of weight loss. Despite these data, only 20% of adults in the United States who are attempting to lose weight report using a combination of energy restriction and engaging in >150 minutes of moderate intensity physical activity per week (28). More details concerning the link between physical activity and reducing the risk of weight gain and obesity may be found in Chapter 10.