[Nutritional intake and bone mineral density in female adolescents]

Adolescence is a critical time in skeletal development, during which the amount of bone gained along with the subsequent rate of bone loss have a crucial impact on an individual's total bone mass in adulthood and old age. Factors believed to influence bone accretion and peak bone mass include adequate nutritional intake, namely for calcium. However, the findings of several studies have raised questions about the benefit of the total dietary calcium consumption for young adult bone health. The objective of this study was to evaluate the association between nutritional intake, namely calcium, and bone mineral density in female teenagers.

The study design was a cross-sectional analysis and data derived from a school-based survey of adolescents from high schools. In all, the study sample included 254 female adolescents with ages between 15 and 17 years. The questionnaire was anonymous and confidential, and provided information on the following variables: bone mineral density (BMD), evaluated in the calcaneus by ultrasound through the Sahara Clinical Bone Sonometer from Hologic; weight and height, measured according to international standards; nutritional intake assessed by a food-frequency questionnaire developed by the Epidemiology Department, Faculty of Medicine, University of Porto; sociodemographic characteristics; age of first menstruation; regularity of menstrual cycles; use of contraceptives and drugs; history of bone fractures; smoking habits; and physical activity. In order to study the association between nutritional intake and BMD, uni and multivariate regression analysis (with adjustment for confounders, namely irregular menses, energy and protein intake) was used.

The following main results were reached: positive and significant effects were found for calcium intake in BMD, even after adjustment for confounders (ss = 0.003, 95% CI = 0.000 - 0.006, p = 0.031); 15.1% of adolescents showed t-scores that suggested osteopenia; mean calcium intake (1229 +/- 778 mg/day) was lower than recommended for optimal bone acquisition in achieving maximal peak bone mass.

Calcium intake was positively associated with BMD, but mean calcium intake was lower tan recommended. It should be therefore important to assure good dietary habits and adequate calcium intake in female adolescents for the development of peak bone mass, and reducing the risk of osteoporosis later in life.