Vitamin D Deficiency and Psychiatric Illness: Supplementation Might Help Patients with Depression, Seasonal Mood Disturbances

In the United States, >50% of psychiatric inpatients have vitamin D deficiency-- Biosynthesis of vitamin D Biosynthesis of vitamin [D.sub.3] begins with the sterol provitamin D3 molecule 7-dehydrocholesterol (Figure, page 20). (2) When skin is exposed to sunlight, 7-dehydrocholesterol absorbs UV radiation and forms provitamin [D.sub.3] which undergoes rapid transformation to vitamin [D.sub.3]. (2) Vitamin [D.sub.3] is released from the plasma membrane and enters systemic circulation in a protein-bound form that has a serum half-life of 36 to 78 hours. (3) Vitamin [D.sub.3] can be taken up by adipocytes and stored in fat deposits, where it has a half-life of approximately 2 months. (4) [FIGURE OMITTED] Circulating vitamin [D.sub.3] is metabolized in the liver by the enzyme vitamin D-25-hydroxylase to 25-hydroxyvitamin D (25[0H][D.sub.3]), which has a serum half-life of approximately 15 days. (4) Circulating 25(OH)[D.sub.3], is not biologically active at the physiological level, and requires activation by conversion to 1,25-dihydroxyvitamin D (1,25[OH]2[D.sub.3]) in the kidneys by the enzyme 25(OH)D-1[alpha]-hydroxylase. Production of 1,25(OH)2[D.sub.3] is regulated by serum phosphorus and parathyroid hormone levels and other factors. (5) Catabolism of 1,25(OH)2[D.sub.3] is rapid, with a serum half-life of 3.5 to 21 hours. (6) Vitamin [D.sub.2] is structurally similar to vitamin [D.sub.3'] but occurs primarily in fungi, yeasts, and some invertebrates. Risk factors for deficiency A patient's vitamin D status is determined by measuring 25(OH)D (Box). Risk factors for vitamin D deficiency include conditions that affect cutaneous production (insufficient sunlight exposure), obesity, gastrointestinal disorders, aging, renal disorders, and medications (Table 1, page 22). (2), (5), (7), (8) The link between sunscreen use, either alone or in cosmetics, and vitamin D deficiency continues to be debated. While controlled studies have found that application of sunscreen with high sun protection factor can significantly reduce vitamin D production, (9) studies in clinical populations have failed to confirm these findings. (10), (11) See this article at CurrentPsychiatry.com for a discussion of these risk factors and acute and long-term medical manifestations of deficiency. [ILLUSTRATION OMITTED] Box Measuring vitamin D levels Although 1,25-dihydroxyvitamin D (1,25[OH]2[D.sub.3]) is the biologically active form of vitamin D, its circulating half-life is only 4 to 6 hours. (a), (b) Therefore. 25-hydroxyvitamin D (25[OH]D) is the principal vitamin D metabolite measured to determine vitamin D status. Vitamin D levels commonly are expressed as ng/mL or nmol/L; the conversion factor from ng/mL to nmol/L is 2.496. The Institute of Medicine has defined vitamin D deficiency as a serum 25(OH) D level of 150 to 200 ng/mL. (a) Source: For reference citations, see this article at CurrentPsychiatry.com Table 1 Risk factors associated with vitamin D deficiency Age (>65) Insufficient sunlight Breastfeeding Dark skin Malabsorption diseases Obesity (BMI >30 kg/[m. …