Vitamin D: what clinicians need to know

Abstract

Recent literature on vitamin D is full of controversies regarding its measurement, benefits, diagnosis, and management of its deficiency. In addition to addressing the consequences of deficiency, benefits of its replenishment, and clinical recommendations for supplements, this review addresses extra-skeletal effects of vitamin D. Vitamin D is essential for skeletal health and prevention of falls and injuries. Vitamin D enhances intestinal calcium absorption and mineralization of osteoid tissues. Rickets in children and osteomalacia in adults are classic manifestations of severe vitamin D deficiency. Cohort studies suggest that low 25 hydroxyvitamin D [25(OH)D] affects numerous and diverse physiologic functions, such as control of cell growth including cancer cells, protection against autoimmune disorders, and muscular coordination. Emerging data also suggest that low vitamin D levels may worsen disorders, including cancer, metabolic syndrome, obesity and diabetes, infectious diseases, and autoimmune disorders. Whether increased incidences of these diseases are consequences of widespread vitamin D deficiency is to be determined. Moreover, many reported relationships between vitamin D deficiency and diseases are based on epidemiological observations. Measurement of serum 25(OH)D is the way to evaluate vitamin D status. Serum 25(OH)D levels below 20 ng/mL are considered deficient, whereas optimum levels are between 30 and 50 ng/mL. An additional 1,000 IU of vitamin D per day generally is sufficient for lighter-skinned individuals; elderly, obese, and dark-skinned individuals and other groups of patients may need an additional 2,000 IU or more per day to maintain physiologic serum 25(OH)D levels.

Vitamin D supplementation guidelines

“…A simple and effective tool to help prevent uncontrolled overuse of vitamin D for healthy population is a guideline for an upper tolerable intake values (upper limit; UL) (16,19,76,78,95). Surprisingly, the upper limit values reported so far are generally agreeable for a given age irrespective of source of reference, Table 2.…”

Vitamin D: an essential component for skeletal health

“…Vitamin D insufficiency encountered in the elderly and institutionalized persons is well documented. 7,[53][54][55] Studies have reported more than half of North American women receiving antiosteoporosis therapies 56 and 88% of women with fractures have serum 25(OH)D levels of less than 20 ng/mL; 57 other studies have confirmed these results. 58,59 Asians living in Western countries and those with African ethnicity have a two-and threefold higher prevalence, respectively, of vitamin D deficiency, than do whites.…”

“…35 Generally, it takes about 7 to 14 days to peak the serum vitamin D level after sun exposure. However, skin elasticity decreases with age, and older people have atrophic skin, which is further aggravated by postmenopausal estrogen deficiency, leading to lesser ability to produce vitamin D. 7 Vitamin D is found naturally in a limited number of foods, such as fatty fish and in irradiated mushrooms. Consequently, vitamin D is added to certain foods, such as milk, yogurt, orange juice, margarine, infant formula, and breakfast cereals.…”

“…However, changing the dietetic pattern or increasing sun exposure to enhance vitamin D levels does not seem practical to many. 7 Thus, proactively identifying those who are at risk for deficiency and treating them with therapeutic doses of vitamin D would be a better, and a more cost-effective option.…”

“…[3][4][5][6] Despite the availability of sunlight, it is estimated that over 2 billion people in the world are vitamin D deficient. 7 Sensible exposure to sunlight and better intake of dietary and supplemental vitamin D could prevent this deficiency in a cost-effective manner.…”