Vitamin D: Giveth to Those Who Needeth

Area of Science:

• Nutritional Science
• Gerontology
• Public Health

Background:

• Severe vitamin D deficiency is linked to rickets.
• Recent meta-analyses have questioned vitamin D's efficacy in preventing elderly fractures, but these studies had methodological limitations.
• Vitamin D deficiency is associated with various chronic diseases, though large trials show no benefit for cardiovascular disease or cancer in generally sufficient populations.

Purpose of the Study:

• To critically evaluate the evidence on vitamin D supplementation for health outcomes.
• To address conflicting findings regarding vitamin D's role in fracture prevention and chronic disease management.
• To determine the benefits of correcting vitamin D deficiency in specific populations.

Main Methods:

• Review and critical analysis of existing meta-analyses and randomized controlled trials (RCTs).
• Examination of studies excluding combined calcium and vitamin D supplementation or using suboptimal dosing.
• Consideration of post-hoc analyses and Mendelian randomization studies.

Main Results:

• Combined calcium and vitamin D supplementation reduces hip and non-vertebral fractures in the elderly, especially those with deficiency or in institutional settings.
• Vitamin D supplementation did not show benefits for cardiovascular disease, cancer, or diabetes in populations with normal baseline levels.
• Evidence suggests vitamin D may prevent upper respiratory infections and has a causal link with lower multiple sclerosis risk; prenatal supplementation benefits mother and child.

Conclusions:

• Methodological flaws in some meta-analyses may have led to underestimation of vitamin D's benefits.
• Correcting vitamin D and/or calcium deficiency is beneficial for infants, pregnant women, and the elderly.
• Further well-designed studies are needed, but current data support addressing deficiencies for improved health.