Simulated sunshine and vitamin D status.
Increasingly health professionals are becoming aware of the numerous roles that Vitamin D plays in the body, particularly in regard to bone health, calcium metabolism, metabolic and immune health. Cutaneous synthesis is an important source of this vitamin, and studies are increasingly showing that numerous populations may not be achieving the recommended levels of Vitamin D (25-dihydroxychocalciferol/25(OH) D) necessary for health. In darker skinned individuals, particularly those living in northern or southern latitudes, increased sun exposure may be necessary to attain Vitamin D sufficiency. This is because the increased melanin pigment in the skin absorbs a high proportion of incident ultra violet B (UVB) light, and thus reduces the stimulation of cutaneous Vitamin D synthesis. Current recommendations in the United Kingdom (UK) suggest that short, casual exposures to summer sunlight contains enough UVB to manufacture adequate levels of Vitamin D. However, studies have demonstrated that such exposure could produce Vitamin D sufficiency in 90% of the white adult population but in none of the study participants who were of South Asian descent. This suggests that different recommendations may be required for different racial and ethnic groups.
Researchers in this study examined the effects of a dose range of simulated summer sunlight exposures in raising Vitamin D status in UK adults of South Asian descent. 60 healthy adults of ages ranging from 20 to 60yr were enrolled in the study. They were randomised to receive one of six doses of IV exposure three times a week for six weeks while casually dressed to reveal 35% skin surface area (approximating the amount of skin revealed in summer whilst outdoors). The doses ranged from 0.65-3.9 standard erythema doses (SED), which were equivalent to 15-90min of unshaded noontime summer sunlight exposure under a clear sky in Manchester, 53.5 degrees north. UV-25(OH)D dose-response relation as well as circulating 25(OH)D outcomes were explored via weekly blood samples.
Subjects also completed daily logs of Vitamin -D containing foods in the first and last weeks of the study to estimate oral Vitamin D intake from foods such as: oily fish, eggs, cheese, oily spreads and oils, milk and milk-containing products and red meat.
In this study circulating 25(OH)D concentration <5[eta]g/mL was defined as deficient, <10[eta]g/mL as being a level with increased risk of osteomalacia and rickets and <20[eta]g/mL as insufficient. Levels [greater than or equal to] 20 [eta]g/mL was defined as sufficient.
Of the 60 subjects, 9 failed to complete the study thus the results of 51 participants were analysed. The mean serum 25(OH)D concentration was significantly higher post-course than at baseline in all groups. Post course there were significantly higher levels in the 3.25SED group than in the 0.65SED and 1.3SED group. Thus the total rise on 25(OH)D correlated positively with the dose of UVB given. As could be expected, levels rose faster in those with lighter skin. With respect to cut-off of Vitamin D sufficiency, only 6 of the total 51 subjects attained the 25(OH)D concentration for sufficiency. These were all in groups receiving higher levels of SED, and only 25% of the individuals in the highest responding dose group attained serum concentrations of [greater than or equal to] 20[eta]g/mL. Interestingly in this study, the highest dose of UV light (3.9SED) was associated with UV-induced epidermal thickening and melanin synthesis which may have reduced cutaneous UVB penetration and therefore failed to produce higher 25(OH)D concentrations than the 3.25SED dose. In addition, there may have been UV generated degradation of Vitamin D in the highest dose group.
Overall the study suggests that a useful gain in vitamin D may be seen in South Asians when exposed to 45 minutes of summer sun at noon (equivalent to 1.95SED) but that higher levels may be optimal (researchers did not expressly state with what amount of time the 3.25SED dose was correlated but it may be assumed to be less than 90 minutes and more than 45 minutes). Researchers note that given the difficulty in obtaining the required amount of sunlight at various times of year, more emphasis should additionally be placed on oral Vitamin D intake in these populations.
Whilst the study was completed in the UK, the results may be applicable to darker-skinned individuals living in the southern regions of Australia, a population group known to be at higher risk of Vitamin D deficiency. Particularly during winter, health professionals should be aware to counsel such clients/patients about the increased need for sunlight exposure and oral intake of Vitamin D.
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|Publication:||Australian Journal of Herbal Medicine|
|Date:||Sep 1, 2013|
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