One-year Change in Spinal Bone Mineral Density in Young Vegetarian and Nonvegetarian Women

Abstract

Cross-sectional spinal bone mineral density (BMD) did not differ between healthy vegetarian and nonvegetarian women with regular menstrual cycles, who were studied while participating in a six-month prospective study of subclinical menstrual disturbances (Am J Clin Nutr 1994;60:887-894). Over that time period, subjects recorded basal body temperature to assess menstrual cycle characteristics and provided 3-d food records in 3 different menstrual cycles. BMD was measured in lumbar vertebrae one through four (Lunar DPX, software version 3.1). The present study was designed to observe the one year change in BMD in the same population. Of 45 women completing the original study, 20 who could be located and had maintained their dietary habits agreed to take part in the follow-up study of BMD. These women did not differ in baseline BMI or BMD from those not restudied. Follow-up BMD measurements were made 1.10±0.08 yr after initial measurements, and changes were adjusted to 1.0 yr. Vegetarians and nonvegetarians were similar in age (x = 29.9±5.2 yr), but vegetarians had lower BMI (21.0±1.5 vs 23.4±2.1 kg/m2, P=0.008). There was no significant weight change over 1 yr in either group (+0.1±2.5 kg for vegetarians and −0.3±2.3 kg for nonvegetarians). For all women combined, BMD increased by 1.2% (1.195±0.129 vs 1.209±0.131 g/cm2, P=0.009). When separated by diet group, there was a 1.9% increase in nonvegetarians' BMO (P=0.004), but no significant change in vegetarians' BMD (0.5%, NS). Changes in BMD were not correlated with mean 9-d nutrient intakes or with menstrual cycle characteristics (that had been determined one year earlier), or with weight change over one year. In conclusion, there was no detectable change in the BMD of vegetarian women over one year, whereas nonvegetarian women experienced a significant increase. The reason for this difference is not apparent. Further prospective research on change in bone density of young vegetarian women appears warranted.Supported by a grant from the B.C. Medical Services Foundation.