Does tobacco use influence bone mineral density levels in a Norwegian youth cohort followed from adolescence to young adulthood? The Fit Futures Study (2010-2022).

Objectives: To investigate the longitudinal associations between tobacco use (smoking and snuff) and bone mineral density (BMD) at femoral sites and in the total body in a Norwegian adolescent cohort, aged 16-27 years.

Design: Prospective longitudinal cohort study.

Setting: A population-based study in Norwegian adolescents from the general population.

Participants: In total, 722 adolescents (385 females and 337 males) with a mean age of 16 years (SD: 0.5) from the Fit Futures Study (FF) were included at FF1 (2010-2011), with follow-up measures at age 18 years (FF2 (2012-2013)) and 27 years (FF3 (2021-2022)). Inclusion criteria were completed dual-energy X-ray absorptiometry (DXA) scans, serum vitamin D blood samples and information on smoking, snuff use, physical activity, height, alcohol intake, hormonal contraceptive use and puberty status, all at baseline (FF1).

Primary And Secondary Outcome Measures: Associations between self-reported smoking and snuff use (categorised as never, sometimes or daily) and changes in BMD (g/cm²) at the total hip, femoral neck and total body, measured using DXA.

Results: Total hip BMD (mean (g/cm), 95% CI) slightly increased from FF1 (females: 1.066, 95% CI 1.054 to 1.079; males: 1.121, 95% CI 1.105 to 1.136) to FF2 (females: 1.076, 95% CI 1.063 to 1.089; males: 1.141, 95% CI 1.126 to 1.157; p<0.001), but thereafter decreased to FF3 (females: 1.050, 95% CI 1.036 to 1.063; males: 1.091, 95% CI 1.074 to 1.107; females and males, both p<0.001). Similar patterns were observed for the femoral neck, while total body BMD increased from FF1 through FF3 (p<0.001). We observed interactions between time and smoking and between time and snuff use in all models (all p<0.001). However, we generally observed no statistically significant differences in BMD levels across smoking and snuff use groups at different time points (all p>0.07), except in females at 18 years (FF2), where those who never smoked had higher total hip BMD than those who sometimes and never smoked (p<0.001).

Conclusions: We found no statistically significant associations between smoking or snuff use and BMD levels in Norwegian adolescents from a median age of 16 to 27 years. Notably, only 2.6% of females and 3.9% of males reported smoking daily. However, in this study, moderate tobacco use did not appear to negatively influence bone growth from adolescence to young adulthood.