Elevated Risk of Osteoporosis for Vegetarian Modified by Smoking and Milk Consumption

Background Vegetarian diets are often linked to health benefits, yet concerns remain regarding potential adverse effects on bone health arising from nutrient deficiencies. Lifestyle factors that can be modified may influence this risk. Methods A cross-sectional study was conducted among adults receiving community health services in Zhunan Township, Taiwan, with a total of 610 participants enrolled. Dietary patterns and lifestyle factors were assessed using structured questionnaires, and bone mineral density was measured. Logistic regression models were applied to evaluate the association between vegetarian diet and osteoporosis, with interaction terms included to examine potential modifying effects of smoking, milk consumption, and coffee consumption. Stratified analyses were performed to further assess the roles of these modifying influences. Results After excluding participants with missing information on dietary pattern or bone mineral density, 573 subjects remained for the final analysis. Vegetarian diet was associated with a significantly higher risk of osteoporosis compared with a non-vegetarian diet with an adjusted odds ratio (aOR) of 3.03 (95% CI: 1.52–6.05). Interaction analysis indicated that smoking (P = 0.0230) and milk consumption (P = 0.0110) significantly modified this association. Among smokers, vegetarians had a substantially higher risk of osteoporosis with an aOR of 48.70 (95% CI: 6.52–363.67). Among those who did not consume milk, the vegetarians also had a greater risk with an aOR of 31.71 (95% CI: 6.72–149.59). Conclusions Vegetarian diet was independently associated with increased risk of osteoporosis, and this risk was particularly elevated among individuals who smoked or did not consume milk. These findings highlight the importance of considering lifestyle factors when evaluating bone health risks in populations adhering to vegetarian diets. Trial registration Not applicable.