Underweight linked to increased osteoporosis risk

Being underweight puts adolescents at risk of osteoporosis in adulthood, and this risk further increases in those who remain underweight in their adult life, according to a retrospective study.

Researchers looked at 1,083,491 adolescents who were examined for mandatory military service between 1967 and 2019. Of these, 65,244 (6.02 percent) were underweight, 821,348 (75.77 percent) had normal weight, 97,801 (9.02 percent) were overweight, and 45,512 (4.20 percent) had obesity.

Over 19,400,208 person-years of follow-up, 28,426 incident cases of osteoporosis were recorded, including 21,497 among women and 6,929 among men. The mean (SD) age at diagnosis was 54.6 years for women and 57.8 years for men.

Adolescent BMI showed a consistent inverse association with osteoporosis risk in adulthood. The crude incidence rate of osteoporosis decreased from 330.2 per 100,000 person-years among those with extreme underweight (<3rd percentile) to 78.9 among those with obesity (≥95th percentile). Across the BMI categories (from underweight to obese), the hazard ratios for osteoporosis ranged from 1.88 (95 percent confidence interval [CI], 1.74–2.04) to 0.83 (95 percent CI, 0.77–0.89) in women and from 1.82 (95 percent CI, 1.64–2.01) to 1.04 (95 percent CI, 0.93–1.16) in men, using normal BMI as the reference.

The risk of osteoporosis varied between the sexes, with obesity showing a protective association in women but not in men.

The highest risk was seen among individuals who remained underweight from adolescence into adulthood.

The findings highlight the importance of having a healthy weight in adolescence in order to prevent osteoporosis, among other diseases, later in life.