Does Chronic Sunscreen Use Reduce Vitamin D Production to Insufficient Levels?

M. Norval; H.C. Wulf

Disclosures

The British Journal of Dermatology. 2009;161(4):732-736. 

In This Article

Abstract and Introduction

Abstract

Exposure to ultraviolet B radiation in sunlight provides the mechanism for more than 90% of the vitamin D production in most individuals. Concern has been expressed in recent years that the widespread use of sunscreens, particularly those with high sun protection factors, may lead to a significant decrease in solar-induced previtamin D3 in the skin, resulting in a vitamin D level which is considered insufficient for protection against a wide range of diseases. In this article the published evidence to support and to question this view is presented. It is concluded that, although sunscreens can significantly reduce the production of vitamin D under very strictly controlled conditions, their normal usage does not generally result in vitamin D insufficiency.

Introduction

As solar ultraviolet (UV) irradiation provides the means for more than 90% of the vitamin D production in most individuals, it is crucial to have sufficient sun exposure to ensure optimal levels of this vitamin. The first step in the production of the biologically active form of vitamin D [1,25-dihydroxyvitamin D3, 1,25(OH)D] is the conversion of 7-dehydrocholesterol (also known as provitamin D) in the skin to previtamin D3 following solar UV radiation (UVR).[1] The action spectrum for this reaction indicates that it occurs in the UVB waveband (290–315 nm) with maximum efficiency at approximately 300 nm.[2,3] Vitamin D3 is then formed from previtamin D3 via a gradual thermal isomerization. Vitamin D3 leaches into the blood and is hydroxylated to 25-hydroxyvitamin D3 [25(OH)D, calcidiol] in the liver. The final step is the synthesis of 1,25(OH)D (calcitriol) in the kidney and other organs. Calcidiol [25(OH)D] circulates in the blood and is the most accurate measure of a person's vitamin D status.

Until recently a 'normal' or sufficient level of 25(OH)D was considered to be 50–250 nmol L−1 (20–100 ng mL−1), insufficient 25–50 nmol L−1, deficient < 25 nmol L−1, excess > 250 nmol L−1 and intoxication > 325 nmol L−1.[1] Information has now become available to indicate that a level of at least 80 nmol L−1 (30 ng mL−1) might be necessary to provide the optimal and full range of the health benefits of vitamin D.[1] It has been estimated in numerous surveys that a considerable proportion of people within a community may be vitamin D deficient or insufficient, including not only the elderly but also children and young adults. Many variables are of importance in determining the extent of previtamin D3 production in the skin as a result of sunlight exposure such as age, skin colour, clothing habits, area of skin exposed and latitude of residence in addition to the season of the year, weather and time of the day.

Protection from the sun has been advised for more than 40 years as solar UVR causes sunburn and is a recognized carcinogen. It is the major risk factor for the nonmelanoma skin cancers (NMSCs) and is implicated in the induction of malignant melanoma. Although NMSC is rarely fatal, melanoma can be and, for example, accounts currently for about 2000 deaths per year in the U.K. The incidence of each of the skin cancers is increasing year by year in populations with fair skin.[4–7] Treatment of skin cancer imposes a huge burden on national health services, estimated at greater than $800 million per year in the U.S.A., and it can be disfiguring for the patient. In addition to tumorigenesis, chronic cumulative solar UVR causes photoageing. There are also immunosuppressive effects, leading to the possibility of a lowered ability to combat microbial infections.

Changes in society in the second half of the 20th century include the fashion for white-skinned individuals to be tanned, to wear minimal clothing as soon as the sun shines and to enjoy holidays in sunny locations, frequently in another country closer to the equator. Health campaigns in several countries have sought to increase public awareness regarding the inherent dangers of sunbathing and, as part of this advice, have recommended that sunscreens should be used.[8–11] These were designed to protect against sunburn rather than against skin cancer, photoageing or photoimmunosuppression but it is likely that some degree of protection against all these effects will occur. Sunscreens are either inorganic, reflecting or scattering UVR, such as zinc oxide and titanium dioxide, or organic, absorbing UVR, such as cinnamates and salicylates.[12] They give different levels of protection against sunburn, ranging from sun protection factors (SPFs) of 6 to > 50. One worry that has been expressed about their widespread and increasing use is that they could prevent or significantly lower the solar UVB-induced production of previtamin D3 in the skin and hence lead to a vitamin D-insufficient or deficient state with reduced protection against a range of diseases. Published evidence to support this view and to question it is presented below.

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