Objective To study vitamin D status and bone metabolism of premenopausal vegetarians and omnivores during a 1-year period.Design Longitudinal, observational study. Bone mineral density was measured, blood samples from fasting subjects were obtained, and 24-hour urinary samples were collected in February 1994, August 1994, and January 1995. Serum 25-hydroxyvitamin D [S-25(OH)D] and intact parathyroid hormone (Si-PTH) concentrations were measured and intestinal calcium absorption was estimated. Dietary intakes of vitamin D and calcium were calculated.Subjects/setting Six vegans, 6 lactovegetarians, and 16 omnivores living in Helsinki, Finland.Statistical analyses performed Student-Newman-Keuls test; unbalanced, repeated-measures multiple analysis of variance; analysis of covariance; Pearson correlation test; and linear regression analysis.Results Dietary intake of vitamin D was significantly lower in vegans (P<.05, yearly mean+/-standard deviation=0.09+/- 0.06 μg/day) and in lactovegetarians (P<.05, 0.7+/-0.4 μg/ day) compared with omnivores (4.0+/-2.1 (μg/day). Throughout the year S-25(OH)D (P=.01) concentrations were lower and S-iPTH (P=.01) concentrations were higher in vegans than in omnivores and lactovegetarians. Bone mineral density in the lumbar region of the spine was lower in vegans (yearly mean+/-standard deviation=1.034+/-0.174 g/ cm 2 ) than in omnivores (P=.05, 1.177+/-0.099 g/cm 2 ) and tended to be lower than that in lactovegetarians (P=.17, 1.138+/-0.06 g/cm 2 ). Bone mineral density in the neck of the femur tended to be lower in vegans (0.843+/-0.116 g/cm 2 ) than in omnivores (P=.07, 0.999+/-0.138 g/cm 2 ) and lactovegetarians (P=.15, 0.961+/-0.059 g/cm 2 ). No seasonal variation was found in bone mineral density in the study groups.Conclusions At northern latitudes, dietary intake of vitamin D in vegans was insufficient to maintain S-25(OH)D and S-iPTH concentrations within normal ranges in the winter, which seems to have negative effects on bone mineral density in the long run.Applications An increase in vitamin D intake should generally be recommended for vegans at least during winter, or selections of foodstuffs fortified with vitamin D should be broadened in northern latitudes. J Am Diet Assoc. 2000; 100:434-441.