Male runners who do not receive enough energy from their diet can be at risk for stress fractures, according to a new study.

The findings of the study will be presented at the Endocrine Society's annual meeting in Atlanta, Ga. "Our findings indicate that male runners, including recreational runners, should be counselled on the importance of adequate nutrition and caloric intake to optimise hormones, body composition, and bone health and to prevent stress fractures," said lead researcher Melanie S. Haines, M.D., of Massachusetts General Hospital in Boston, Mass.

Female athletes with undernutrition are at risk for low bone density and stress fractures, Haines noted. "However, it is unclear whether a similar process occurs in male athletes," she added.

The researchers enrolled 15 male runners and 16 male non-athlete controls, aged 16-30 years. They assessed their bone density, body composition and blood hormone levels. They found that bone density of the tibial cortex, or outer shell of bone of the lower leg, was lower in athletes than in controls.

This may increase the risk for stress fractures in male runners, which occur in this outer shell of bone. Lower weight and muscle mass, and lower levels of a hormone associated with fat mass (such as leptin and estrogen) were associated with lower bone strength in the lower leg.

"We suspect that a subset of male runners may not be fueling their bodies with enough nutrition and calories for their high level of physical activity. The undernutrition that results negatively affects hormones and bone. Just getting enough calcium and vitamin D is not enough to overcome other macronutrient and micronutrient deficiencies," Haines notes.

Hormones are very important for bone health and strength. Abnormal hormone levels in the body can contribute to low bone density and increased fracture risk. The Endocrine Society recognises that there are a number of risk factors for poor bone strength in young men, including low body weight or losing too much weight, diets low in calcium, low vitamin D and testosterone levels, and eating disorders.