Oral contraceptives, other factors reduce bone mass

Oral contraceptive use and loss of normal menstrual function may negatively impact bone health, according to a study of female military cadets.

By contrast, "greater amounts of exercise and increased milk intake were found to be important to skeletal health," co-investigator Dr. Jeri Nieves told Reuters Health.

Nieves, of Columbia University in New York City and Helen Hayes Hospital, West Haverstraw, New York, and colleagues looked at associations between lifestyle, diet, and exercise factors and bone health in 107 female Caucasian cadets who averaged 18.4 years of age upon entering the United States Military Academy in West Point, New York.

The researchers compared the cadets' previous year's exercise; their consumption of milk, yogurt, cheese, and calcium containing vegetables; as well as caffeine, alcohol, and tobacco; and their lifetime history of fractures, age at first menstruation and menstrual frequency, and current and prior use of oral contraceptives.

Nieves and colleagues compared this information, combined with cadets' body height, weight, and fitness measures, to determine if any of these factors were associated with bone strength and size, as measured in the tibia bone of the lower leg, and at the spine, hip, and heel.

Overall, the cadets had healthy lifestyles, the researchers report in the journal Nutrition and Metabolism. Cadets' daily calcium intake was 1000 mg, about equal to the recommended daily intake for their age group; 97 percent were tobacco free; and 77 percent exercised more than 7 hours weekly. Eleven percent reported current oral contraceptive use.

Measurements of bone mineral density and strength indicated greater bone health among more fit cadets and those reporting a higher milk intake.

"A loss of normal menstrual function was found to have a detrimental impact on the skeleton and, in these young adults, oral contraceptives also had a negative impact on the skeleton," Nieves said.

"Peak bone mass, the maximum bone density a person will ever have, is attained by age 25," Nieves said.

"It is important to maximize peak bone mass to prevent stress fractures in young adults and osteoporosis in later life," she added.

SOURCE: Nutrition and Metabolism, August 2007