Physical activity, nutrition, and reproduction.

Abstract

Thin high mileage female and male runners often have reproductive problems. Strenuous physical activity can affect the hypothalamic-pituitary-gonadal (HPG) axis function of both females and males but physical activity alone probably does not cause reproductive problems. Nutritional changes and changes in the metabolic balance are likely responsible for the exercise-associated reproductive problems. Reproductive dysfunction in female athletes include pubertal delay (age at menarche 15.5 years for ballet dancers 15 years for athletes trained before menarche vs. 12.5 years for controls) luteal phase inadequacy anovulatory cycles secondary amenorrhea and oligomenorrhea. Male athletes tend to have reduced circulating testosterone androstenedione and luteinizing hormone levels. Endurance training has comparable chronic effects on the HPG axis in women and men. A possible mechanism of inhibition is changes to the gonadotropin releasing hormone-gonadotropin axis the cause of the changes is unknown. Neurotransmitter precursor deficiencies changes in thyroid function activation of stress hormones changes in glucoregulatory and other metabolic hormones changes in steroid metabolism in fat tissue changes in hepatic metabolism of binding proteins or an exaggerated peripheral response to exercise in a nutritionally stressed person are possible causes of the changes to the axis. Factors in the emergence of exercise-associated menstrual dysfunction include the physical and emotional stress of training and/or competition predisposition to menstrual irregularity inadequate nutrition weight loss and low body fat. Reduced physical activity reverses menstrual dysfunction. Further research is needed to clarify the relative importance of dietary deficiencies energy balance and physical activity in bringing about reproductive change and dysfunction. Obstacles to resolving the complex interrelationships are imprecision of dietary evaluation difficulty of accuracy versus freedom in energy balance measurements and the conceptual barrier of the body fat theory.