Emerging nutritional and lifestyle risk factors for bone health in young women: a mixed longitudinal twin study

Late adolescence and early adulthood are times of major behavioral transition in young women as they become more independent and make choices about lifestyle that will affect their long-term health. We prospectively evaluated nutritional and lifestyle factors in 566 15 30-year-old female twins participating in a mixed longitudinal study of diet and lifestyle.Twins completed 790 visits including questionnaires and measures of anthropometry. Nonparametric tests (chi-square, Mann-Whitney U, and Kruskal-Wallis; SPSS) were used to examine age-related differences in selected variables. Dietary calcium intake by short food frequency questionnaire was relatively low [511 (321,747)] mg/day (median, IQR; 60 % of estimated daily total) and did not vary significantly with age. The number of young women who reported ever consuming alcohol (12+ standard drinks ever) increased from 50 % under 18 years to 93 99 % for the 18+ age groups. Of those who consumed alcohol in the preceding year, monthly intake doubled from under 18 years (5.7, 3.9, 19.0 standard drinks; median, IQR) to 18+ years (12.0, 4.7, 26.0; P < 0.001) with the highest consumers being 21 23 and 27 29 years. At age 15 17 years, 14 % reported ever smoking and by age 27–29, 51 % had smoked (P = 0.002). Under the age of 20 years, average cigarette consumption in smokers was six cigarettes per day, increasing to ten above age 20 (P < 0.001). Participation in sporting activity decreased with age (P < 0.001): 47.5 % of 15–17-year-olds undertook 4 or more hour/week of sport, compared with 23.5 % at age 27–29 years. Conversely, sedentary behavior increased with age: 25.0 % of 15–17-year-olds reported 1 or less hour/week of exercise compared with 50.0 % at age 27–29 years. BMI increased with age (P = 0.011), from 21.3 (19.5, 23.6; median, IQR) in the youngest to 23.1 (21.5, 25.9) in the oldest. These highly significant changes in behavior in young women as they transitioned into independent adult living are predicted to impact adversely on bone and other health outcomes in later life. It is crucial to improve understanding of the determinants of these changes and to develop effective interventions to improve long-term health outcomes in young women.<br />