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Aging decreases the capacity of human skin to produce vitamin D3. MacLaughlin J, Holick MF. J Clin Invest. 1985 Oct;76(4):1536-8. PMID: 2997282

Aging decreases the capacity of human skin to produce vitamin D3. MacLaughlin J, Holick MF. J Clin Invest. 1985 Oct;76(4):1536-8. PMID: 2997282 doi:10.1172/JCI112134 An evaluation of surgically obtained skin (age range, 8-92 yr) revealed that there is an age-dependent decrease in the epidermal concentrations of provitamin D3 (7-dehydrocholesterol). To ascertain that aging indeed decreased the capacity of human skin to produce vitamin D3, some of the skin samples were exposed to ultraviolet radiation and the content of previtamin D3 was determined in the epidermis and dermis. The epidermis in the young and older subjects was the major site for the formation of previtamin D3, accounting for greater than 80% of the total previtamin D3 that was produced in the skin. A comparison of the amount of previtamin D3 produced in the skin from the 8- and 18-yr-old subjects with the amount produced in the skin from the 77- and 82-yr-old subjects revealed that aging can decrease by greater than twofold the capacity of the skin to produce previtamin D3. Recognition of this difference may be extremely important for the elderly, who infrequently expose a small area of skin to sunlight and who depend on this exposure for their vitamin D nutritional needs.

Evidence for alteration of the vitamin D-endocrine system in obese subjects. Bell NH, Epstein S, Greene A, Shary J, Oexmann MJ, Shaw S. J Clin Invest. 1985 Jul;76(1):370-3. PMID: 2991340 The results provide evidence that alteration of the vitamin D-endocrine system in obese subjects is characterized by secondary hyperparathyroidism which is associated with enhanced renal tubular reabsorption of calcium and increased circulating 1,25(OH)2D. The reduction of serum 25-OHD in them is attributed to feedback inhibition of hepatic synthesis of the precursor by the increased serum 1,25(OH)2D.