Medicine & Science in Sports & Exercise:
Roundtable Consensus Statement
Physical activity in the prevention and treatment of other morbid conditions and impairments associated with obesity: current evidence and research issues
RISSANEN, AILA; FOGELHOLM, MIKAEL
Helsinki University Central Hospital, Helsinki, FINLAND; and Lahti Research and Training Centre, University of Helsinki, Lahti, FINLAND
Address for correspondence: Aila Rissanen, Obesity Research Unit, P.O. Box 446, 00029 HUCH, Helsinki, Finland. E-mail: firstname.lastname@example.org.
Roundtable held February 4–7, 1999, Indianapolis, IN.
RISSANEN, A. and M. FOGELHOLM. Physical activity in the prevention and treatment of other morbid conditions and impairments associated with obesity: current evidence and research issues. Med. Sci. Sports Exerc., Vol. 31, No. 11, Suppl., pp. S635–S645, 1999.
Purpose: To evaluate the current status of knowledge concerning the effects of physical activity in the treatment and prevention of obesity- related problems, including cancers of the colon, breast, uterus, and prostate; gallstones; osteoarthritis; back pain; sleep apnea; reproductive abnormalities; and impaired health-related quality of life.
Design: A Medline literature search on the effects of physical activity in the above conditions was conducted. Only studies with some measure of weight and a description of the type of physical activity were included.
Results: No controlled randomized trials of exercise in the treatment of any of the studied conditions in obese patients were identified. Most of the epidemiologic studies reviewed were beset with severe methodological weaknesses. Most of the 18 studies on physical activity and colon cancer risk showed a protective effect that in some studies appeared to be greater than expected by weight loss alone. Some but not all studies of hormone-dependent cancers and gallstones showed a protective effect for physical activity. There were insufficient data on the role of exercise for the other morbid conditions studied.
Conclusion: The scarce data available on the role of physical activity in the prevention of obesity-related chronic conditions listed above suggest a protective role that needs to be examined further in studies with improved methodologies. Well-designed intervention trials are needed to assess the role of physical activity in the treatment and long-term outcome of obese patients with these co-morbid conditions.
Obesity and sedentary lifestyle are associated with a number of chronic disabling conditions. This review covers the knowledge on the role of physical activity in some of these conditions and discusses the problems inherent to studies addressing the complex interrelationships between lifestyle variables and their consequences to health.
An excess risk of postmenopausal breast cancer has been documented for obese women, especially for those with increased abdominal fat (103). Adult weight gain predicts the risk of postmenopausal breast cancer (35). Clinical studies agree that obesity worsens the prognosis of breast cancer in both pre- and postmenopausal women (36). Few studies have been able to disentangle the effects of obesity from those of diet, nutrition, and physical exercise (60).
There is some evidence that physical activity may reduce breast cancer risk in both pre- and postmenopausal women. Most but not all of the several epidemiological studies, all beset with methodological problems, suggest a protective effect of physical activity (44). Although the effect of body mass index (BMI) has been taken into account in the analyses of several studies (Table 1), it is not clear to what extent the protective effect of exercise is independent of body weight. The possible biological mechanisms behind the protective effect include reduction in body weight and in endogenous steroid exposure, changes in growth factors, and enhancement of natural immune mechanisms (78).
Given the biological plausibility and the strength of the evidence from the literature, prevention of obesity and weight gain in adulthood and regular physical exercise could be expected to help reduce the risk of postmenopausal breast cancer in obese women. However, public health recommendations cannot be made on the basis of the existing evidence. Similarly, insufficient data are yet available about the potential benefits of physical activity in weight control after breast cancer has been diagnosed and during treatment.
Increased physical activity may reduce the risk of postmenopausal breast cancer in overweight and obese women. (Evidence category C)
Several studies have documented a positive relationship between obesity and colon cancer and colon adenoma in both men (25) and women (57), but the findings are not fully consistent (79). The excess risk is most evident with abdominal adiposity (57) and with adolescent obesity (79).
Several case-control and cohort studies have consistently shown that physical activity decreases the risk of colon cancer (Table 2). Some of these studies suggest a dose-response relation between increasing level of activity and decreasing level of cancer risk. Overall, an about 50% reduction in cancer incidence has been observed among subjects with the highest level of physical activity across many studies with heterogeneous designs and variable measures of physical activity, including either occupational or leisure time activity or both. The observed relation is stronger for the distal colon and weak or nonexistent for rectum. Although confounding cannot be fully ruled out, the protective effect appears to persist after controlling for other lifestyle factors, including BMI, diet, and alcohol consumption. The proposed mechanisms include reduced bowel transit time and changes in insulin or prostaglandin metabolism resulting from increased physical activity (7).
The evidence of a strong inverse relationship between physical activity and risk of colon cancer seems unequivocal enough to justify the public health message that modest increases in physical activity of the population will help reduce the incidence of colon cancer.
Increased physical activity reduces the risk of colon cancer in overweight and obese men and women. (Evidence Category C)
The risk of endometrial cancer is associated with increased weight and body size (27). There are several case-control studies showing that inactivity is associated with an increased risk of endometrial cancer even when BMI is taken into account (Table 3). However, confounding by diet and other factors hamper the interpretation of these data.
Physical inactivity increases the risk of endometrial cancer in obese women. (Evidence Category C)
Overweight is a risk factor for prostate cancer. The findings concerning the role of physical activity are controversial. Some case-control (97) and cohort studies (26,78) in which allowance has been made for BMI show no relationship between physical activity and prostate cancer, whereas some cohort studies (1,48,67) show a protective effect. A protective effect of exercise against benign prostatic hyperplasia has been observed in the U.S. Health Professionals Study, but the results were not controlled for weight (70).
Research priorities concerning the role of physical activity in obesity-related cancers
Most epidemiological studies of cancer, obesity, and physical activity to date are beset with major methodological weaknesses, including problems in assessing physical activity and inadequate control of confounding factors. Because of the complex interrelationships between lifestyle variables, large long-term cohort studies are needed with careful designs, including proper definition and size of the study population, maintenance of high response rates, and improved and standardized methods of measuring factors linked to lifestyle and behavior.
It is not known whether the type, intensity, and timing in life cycle are important determinants of the protective effect of physical activity. There is a need for better assessment of the mode, intensity, and timing of physical activity in both observational and intervention studies.
There has been little research on the effects of physical activity and weight reduction on the progression of hormone-dependent cancers and colon cancer. Long-term RCT of exercise and dietary intervention in patients with these cancers are needed.
The risk of gallstones increases with adult weight (12) and weight gain and is also related to central location of fat (61). Rapid weight loss is a strong predictor of gallstone formation, especially in women (54). The early studies on the role of physical activity in gallbladder disease (3,20,37,38,74,89,96) yielded controversial results, whereas most later studies suggest a protective effect for physical activity (Table 4). A distinct protective effect of physical activity against the development of symptomatic gallstones was recently observed in the U.S. Health Professionals Study (50). The findings suggest that symptomatic gallstone disease could be prevented by physical exercise even beyond its benefit for control of body weight. The mechanisms by which exercise may influence gallstone pathogenesis are poorly understood (94).
The protective effect of exercise against gallstones has been documented in the U.S. male population. Large-scale, high-quality epidemiological studies on well-defined patterns of physical activity (see section on research priorities in cancers) are needed to evaluate the effects of exercise in women and in other populations.
Also, RCT are needed to assess whether physical activity can prevent the formation of gallstones in obese people during and after weight reduction.
Obesity is a strong risk factor of osteoarthritis of the knee (14,16,56) and the hip (7,11). Excess weight contributes to disability in patients with osteoarthritis (95). Weight loss reduces the risk of developing knee osteoarthritis (15), but its effect on the progression of the disease is unknown.
Some studies suggest that vigorous physical activity may predispose to osteoarthritis by the means of mechanical insult to the joint (9,16). An increased risk has been associated with strenuous sports (41) and with competitive but not recreational running (43). A beneficial effect of physical exercise in the prevention of osteoarthritis has not been demonstrated in any study thus far. Both physical exercise therapy (11) and weight reduction (58) may alleviate the symptoms of arthritis, but few studies have addressed the simultaneous effects of these modalities. One small uncontrolled study combining exercise with weight reduction (10) suggested that physical exercise may help preserve lean body mass during weight loss in obese patients with rheumatoid arthritis, but no effect of symptoms was observed in this study.
Obesity and low physical activity are among the proposed risk factors of low back pain, but the findings are controversial (30,49,100). While many RCT show therapeutic benefits of exercise (17,65,66) and deleterious effect of bed rest (55) in the treatment of back pain, the evidence of benefits of physical activity in back pain is equivocal (13,55).
The evidence of benefits of physical activity, beyond the effect on body weight regulation, in the prevention and treatment of osteoarthritis and back pain is inconclusive. Given the public health importance of these conditions and the theoretical benefits of weight control and physical exercise in these conditions, more research in this area is needed.
Research priorities concerning the role of physical activity in obesity-related musculoskeletal disorders
The research priorities concerning the role of physical activity in obesity-related musculosceletal disorders are as follows:
1. High-quality epidemiologic studies are needed to assess the preventive potential of physical activity and its various dimensions, including types of activity, intensity, duration, frequency, changes in activity levels over time for various chronic disease and functional end points, including arthritis and low back pain. These studies should be designed to take into account and explore the complex interrelationships between physical activity, body weight, lifestyle, diet, and health.
2. Intervention and observational studies of weight loss with various dimensions of physical activity as defined above in the progression of established osteoarthritis of the knee and hip are needed.
3. RCT to test the hypothesis that certain types of exercise would be beneficial during weight reduction in patients with osteoarthritis.
Obesity is a risk factor for obstructive sleep apnea (101), which improves by weight reduction (87). Exercise could improve sleep apnea by facilitating weight loss and also perhaps by stimulating the respiratory drive. In an uncontrolled trial of 11 patients, a 2-h supervised exercise session twice weekly for 6 months improved the symptoms of sleep apnea although the body weight remained unchanged (63).
Obesity is associated with reproductive disorders including polycystic ovary syndrome, menstrual disorders, infertility, miscarriage, and pregnancy complications. These problems are ameliorated by weight reduction (64). We identified no studies that have specifically examined the relationship between these conditions and physical activity in obese patients.
RCT are needed to test whether exercise alone or combined with weight reduction by diet is effective in the treatment of sleep apnea in obese subjects and in normalizing reproductive abnormalities in obese women.
HEALTH-RELATED QUALITY OF LIFE
Obese persons often have limitations in psychological and physical well-being and in other aspects of the day-to-day life, often summarized under the multidimensional concept of health-related quality of life (HRQL) (29,75,86). Weight reduction appears to improve some dimensions of HRQL (76), but the few data are difficult to interpret, especially in less severe obesity (76).
Physical activity improves several aspects of HRQL (71), including psychological and physical functioning and perceived health (84). Some uncontrolled trials (22,28,45,72) have shown an improvement of mood and HRQL in obese patients in weight loss programs with exercise, but the possible independent contribution of exercise cannot be determined from these studies. Exercise has also been reported to be useful in the treatment of binge-eating disorder (52).
RCT are needed to determine whether physical activity improves the various aspects of health-related quality of life beyond its effect of weight loss. Valid assessment of HRQL should be included in all intervention studies of obese persons.
Also, RCT are needed to study the effects of physical activity in binge eating disorder.
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EXERCISE; LEISURE TIME ACTIVITY; OCCUPATIONAL ACTIVITY; COLON CANCER; BREAST CANCER; ENDOMETRIAL CANCER; PROSTATE CANCER; OSTEOARTHRITIS; BACK PAIN; GALLSTONES; SLEEP APNEA; HEALTH-RELATED QUALITY OF LIFE
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