Barriers to optimizing vitamin D3 intake for the elderly

Available data on metabolic utilization of vitamin D₃ indicate a total daily requirement of ∼4000 international units (IU) (100 μg) or twice the current tolerable upper intake level (UL). In young individuals, most of this comes from the skin. However, cutaneous vitamin D₃ synthesis declines with age, creating a need for increasing oral intake to maintain optimal serum 25-hydroxyvitamin D [25(OH)D] concentrations. Estimates of the population distribution of serum 25(OH)D values, coupled with available dose-response data, indicate that it would require input of an additional 2600 IU/d (65 μg/d) of oral vitamin D₃ to ensure that 97.5% of older women have 25(OH)D values at or above desirable levels. The age-related decline in cutaneous input, taken together with the UL, creates a substantial barrier to the deployment of public health strategies to optimize vitamin D status in the elderly.