Associations between macronutrient content and serum vitamin D in the OMNI-Heart Trial

Background: Vitamin D deficiency may be a common problem in adults which could increase the risk of osteoporosis and fracture in later life. Research is being conducted regarding vitamin D's role in decreasing the risk of many chronic illnesses.

Objective: To assess the effect of three diets that differ in macronutrient content, but are otherwise similar, on serum vitamin D.

Design: The OMNI-Heart Trial was a two-center randomized cross-over feeding study of three diets. One was rich in carbohydrates, one in protein (about half from plant sources), and the third, in unsaturated fat, primarily monounsaturated fat. The participants received all their food during the study. Participants ate all three diets in random order.

Results: Serum vitamin D was low in our participants at baseline. In males, average vitamin D was 25.2 ng/ml (white males, 29.6 ng/ml; black males, 20.3 ng/ml; p-value for difference<0.001). In females, it was 22.9 ng/ml (premenopausal females, 17.9 ng/ml; postmenopausal females, 24.8 ng/ml; p-value for difference<0.01). These levels are considered by some experts to be “insufficient” to maintain, for example, adequate intestinal calcium absorption. An unexpected finding was that vitamin D decreased on all three diets except, in premenopausal females.

Conclusions: Although it appears that much of vitamin D synthesis occurs via sun exposure, diet plays a factor. Given that our generally healthy adult participants had low serum vitamin D at baseline which was not improved in most participants during the study, more research should be conducted regarding dietary effects on serum vitamin D.