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Editorial |
Miami Children’s Hospital
Miami, FL
With growing evidence that our population is sedentary and that a healthy life-style is partially dependent on regular physical activity and appropriate nutrition, a recent report by the American Medical Association sets forth a position emphasizing the protective effects of exercise against several chronic diseases [1]. The report also relays the information that as many as 250,000 deaths per year in the United States are attributable to lack of exercise. Several studies have demonstrated that habitual physical inactivity and poor physical fitness are associated with increased mortality rates. Coronary heart disease risk factors have been reduced with regular exercise. Moreover, other outcomes such as increased bone density and more desirable body composition have been linked to nutrition and exercise [2].
In this issue of the JACN, we have compiled a group of important papers which address mineral and bone metabolism in various forms and their relationship with physical activity. Nutrition and physical activity play an important role in the development and achievement of peak bone mass. Calcium and its effect on bones has been receiving most of the attention. This appears clearly in the first report of the newest Dietary References Intakes (DRI), released in August 1997, that deals with calcium and related nutrients, including vitamin D, magnesium, phosphorus and fluoride [3]. Overall, increased higher calcium intakes are recommended for many life-stage groups. For children and most adults, calcium recommendations are based on intakes consistent with maximal calcium retention. Maximal calcium retention is associated with increased bone mass and reduced risk of osteoporosis.
As discussed by Duff and Whiting [4], it is also important to take into consideration the calciuric effects of dietary factors that might have detrimental effects on bone health by affecting calcium retention. It is important to know this aspect when recommending a healthy diet for children in order to maximize their genetic potential for bone mass. In a different age group, Sullivan et al describe the beneficial effects of proper nutritional support with enteral feedings in a population hospitalized for an acute hip fracture requiring surgery [5]. Unfortunately, at a time when calcium recommendations are increased, many Americans fail to consume enough calcium to meet even the previous lower calcium recommendations. According to 1994–1995 data from USDA’s Continuing Survey of Food Intakes by Individuals, less than 35% of all Americans are meeting the 1989 RDAs for calcium.
Numerous studies have shown the positive effects of physical activity on bone mass. Also, even in children, the positive effects of moderate weight bearing exercise on bone mineral density is well known [6]. In this issue, Ilich et al provide extensive data on the determinants of bone mass in preadolescent females with strong evidence of the influence of body composition and physical activity on bone parameters [7]. On the other hand, a certain degree of physical activity may have a negative effect on bone health and could be related to a higher incidence of complications like stress fractures. In the paper of Cline et al it is interesting to note that the incidence of stress fractures in a population of female Army recruits was not associated with decreased bone density, nor with reported calcium intake during adolescence or with adolescent sport participation [8]. Paradoxically, athletes who need to maintain a certain weight for competition may be even at a greater risk following extreme weight loss measures which can impair both performance and health. Delayed puberty and amenorrhea also may occur in female athletes who train intensively or maintain low body weight. Amenorrhea, especially when combined with inadequate calcium intake, can reduce the bone mineral content, thus increasing the risk of stress fractures and osteoporosis in later years [9].
In conclusion, the medical community needs always to be aware that in an attempt to optimize performance, athletes become susceptible to many nutritional misconceptions. Many athletes believe that vitamin, mineral, or protein supplements will help athletic performance, despite evidence to the contrary. Despite expansion of knowledge in the field of nutrition and exercise, a basic premise still appears to hold true—there is little reason for the physically active person’s diet to deviate substantially from that of other healthy persons.
Received January 1, 1998. REFERENCES
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