NEW YORK (Reuters Health) - Men who are slimmer in middle age are at greater risk of having osteoporosis later in life, a new study confirms.

And while losing weight between one's 40s and 70s increased osteoporosis risk, weight gain reduced it, Dr. Haakon E. Meyer of the University of Oslo in Norway and colleagues found.

"Although weight gain and high body weight might be beneficial for the skeleton, a stable, healthy weight is recommended for overall purposes," Meyer and his team write. "However, when considering weight loss interventions, the effect on osteoporosis and fracture should also be included and, if possible, counteracted."

Losing weight and being thin are both known risk factors for the brittle bone disease, the researchers note in the American Journal of Epidemiology. To understand the long-term effects of body weight and weight change in men, they looked at data from 1,476 men who had undergone health screenings in Oslo and Tromso, Norway, in the 1970s and again in 2000 and 2001.

Men in Oslo were 47 to 49 years old at the first screening and 75 to 77 at the second; for the Tromso survey, ages at the first screening ranged from 20 to 50 and from 47 to 76 at the second screening.

Men's body mass index (BMI) at the first screening was related to their bone mineral density (BMD) at the second, Meyer and colleagues found. BMI is a standard measure of how fat or thin a person is.

Among people who had lost 10 percent or more of their body weight between the two screenings, 15.1 percent had osteoporosis, compared to 0.6 percent for those who had gained 10 percent or more.

For individuals who were in the lowest fourth for BMI at the beginning of the study, 31 percent developed osteoporosis if they lost 5 percent or more of their body weight, compared to 4 percent of those who gained 5 percent or more, the researchers found.

Changes in weight can affect bones through several mechanisms, such as stress on the bones from muscle and mechanical loading, hormonal changes that alter bone metabolism, or changes in eating habits.

The researchers were not able to look at the risk of hip fracture in the study participants, but they note that "increased risk is first and foremost seen in persons with BMI less than 25."

They say studies on the long-term effects of weight and weight change on the risk of hip fracture are needed.

SOURCE: American Journal of Epidemiology, August 15, 2008.

• More News on Osteoporosis
• More News on Weight Control

Related MedlinePlus Pages:

• Osteoporosis
• Weight Control