Vitamin D intake and mental health-related quality of life in older women: The Iowa Women's Health Study

Objective: Vitamin D deficiency and mood disorders are both prevalent among the elderly. We evaluated the association between vitamin D intake and mental health-related quality of life (QOL) among elderly women participating in a large population-based study. Study design: This study was a cross-sectional analysis of the Iowa Women's Health Study, a prospective study of cancer risk factors among post-menopausal women in Iowa that began in 1986. Additional survey data was collected from the cohort members in 1987, 1989, 1992, 1997, and 2004. Data for this analysis came from the 2004 questionnaire. Main outcome measure: Mental health-related QOL was assessed using five scales from the Medical Outcomes Study 36-item Short-form Health Survey. QOL scores were analyzed as continuous variables using linear regression, controlling for age, energy intake, BMI, education, smoking, living arrangement, antidepressant usage, comorbidity history, and physical activity. Results: Low vitamin D intake (<400 IU/day) was associated with poorer QOL scores compared to women with higher intake (≥400 IU/day). Differences in QOL scores by vitamin D intake group were attenuated with multivariable adjustment, but a significant overall association between vitamin D and QOL scores persisted. Further adjustment for physical activity attenuated all differences as well as the overall association between vitamin D and QOL scores. Conclusions: Women who consumed <400 IU/day of vitamin D had significantly lower mental health-related QOL compared to those who consumed ≥400 IU/day. Meeting dietary vitamin D recommendations is a potential method for improving QOL among the elderly.