Assessment of Plasma 25-Hydroxyvitamin D Response to Ultraviolet Irradiation over a Controlled Area in Young and Elderly Subjects

Abstract

1.The response of 25-hydroxyvitamin D [25-(0H)Dl to artificial ultraviolet irradiation applied to a known area of dorsal skin was investigated in 18 subjects, small quantities of ultraviolet energy being used. Ultraviolet irradiation was administered on days, 1,3,5,8, 10, 12, 15 and 17, a total of 15 min being delivered over this time. In 15 subjects plasma 25-(0H)D showed a significant increase after a total of 15 min exposure but three subjects failed to demonstrate any increment. Plasma 25-(0H)D did not increase in any subject after 2.5 min of ultraviolet irradiation (irradiation on days 1 and 3).2. Responses were compared in young and old, in male and female and in normal and osteomalacic subjects. No significant difference in response was found between these groups.3. When plasma volume was taken into account, it was possible to calculate the increase in nmol of plasma 25-(OH)D/cm2 skin irradiated. This was 0.024 nmol/cm2 with no sex difference, over the 17 days of irradiation.4. Exposure to ultraviolet irradiation over a small area of dorsal skin led to a rapid rise of plasma 25-(0H)D in most subjects with a subsequent plateau in subjects studied for up to 15 min total exposure. This contrasted with the prolonged increase in plasma 25-(0H)D continuing over several weeks in response to whole-body ultraviolet irradiation. This may indicate that cutaneous synthesis of vitamin D is rapid but limited, and that the considerable rise in plasma 25-(0H)D during whole-body irradiation may originate from vitamin D synthesized during the first few exposures. Abbreviation: 25-(OH)D, 25-hydroxyvitamin D. 235 0143-5221/80/03023s-08s1.s0/1

Aging decreases the capacity of human skin to produce vitamin D3.

“…Because they did not have younger subjects in their study for comparison, they warned that care should be taken in applying their results to a younger population, for there was some evidence that 25-hydroxylation of vitamin D declines with age. Davie and Lawson (15) found that plasma 25-OH-D concentrations increased to comparable levels in a group ofyoung and old subjects who received multiple exposures of ultraviolet radiation either over an area 600-900 cm2 on their backs or over their entire bodies. Despite these findings, it remains a fact that the elderly are more at risk for developing vitamin D deficiency and osteomalacia (1-7, 9-12, 14, 15).…”

“…Hence, although the elderly are able to photosynthesize previtamin D3, their capacity to do so is markedly diminished when compared with that of a young person. Therefore, if the elderly frequently expose a significant area of skin (such as sunbathing in a swimming suit) to sunlight, they probably can maintain adequate vitamin D nutriture without dietary vitamin D3, as suggested by the studies of Davie and Lawson ( 15). For those elderly, however, who do not obtain adequate vitamin D nutrition from their diet and who infrequently expose a very small area of skin (such as hands and face) to sunlight, the greater than twofold decline in their epidermal stores of 7-dehydrocholesterol may very well put them at risk for development of vitamin D deficiency and osteomalacia.…”

“…Despite these findings, it remains a fact that the elderly are more at risk for developing vitamin D deficiency and osteomalacia (1-7, 9-12, 14, 15). It was suggested that this is a result of the failure of aged individuals to go outdoors or from the possibility that the skin of an aged individual requires a greater dose of ultraviolet radiation to synthesize vitamin D3 (15). Because vitamin D is absolutely essential for the development and maintenance ofa healthy skeletal structure in humans, those who do not obtain adequate vitamin D nutrition from their diet must obtain this essential hormone from exposure of the skin to environmental sunlight.…”

Deficiencia de vitamina D en la práctica clínica pediátrica

“…52 Esto ha llevado a la recomendación poblacional de la exposición a la luz solar por 15 minutos, al menos, tres veces a la semana para cubrir los requerimientos de la vitamina; sin embargo, se requieren estudios similares en niños y adolescentes para validar esta sugerencia. En caso de ausencia a la exposición solar (ej.…”

Vitamin D: metamorphosis from nutrient to hormonal system

“…There are, as yet, few available measurements of plasma calciferol in man; in Canadian adults in winter, a mean total plasma calciferol of 2.2 pg/1 (5.7 nmol/l) was associated with a mean total plasma 25-(OH)D of 16 pg/l (40 nmoV1) (Jones, 1978). Davie & Lawson (1980) have estimated the cutaneous production of cholecalciferol following a total of I 5 min U.V. irradiation of restricted areas of human skin over a period of I 7 d. On the basis of the measured increment of plasma 25-(OH)D in the subjects irradiated, they calculate an epidermal production of cholecalciferol of 0.024 nmol/cm2.…”