Atopic Dermatitis: a Short Summary
Sun Exposure and Vitamin D (VitD) Requirements (For Professionals)
Is sun exposure enough to meet daily requirements ?
- Excessive skin exposure is detrimental but in 20 years of stigmatizing sun exposure it is now widely accepted that vitamin D deficiency leads to bone disease and internal skin cancers. Some societies such as osteoporosis societies encourage sun exposure.
- On the other hand, there is no doubt that sun UV radiation leads to skin aging and skin cancer.
Where do our daily vitamin D requirements come from ?
- the major source is the sun.
- the minor source is food. Nowadays lots of foods are fortified with vitamin D such as milk, orange juice…
So what is the adequate recommended time and surface we should expose daily to the sun ?
- According to Dr Horlick: “Expose 25% of the total body surface area (TBSA) to 25% of the minimal erythemal dosa (MED), two or three times a week”.
- This corresponds to 5 to 15 minutes for phototypes I-IV in the summer and 15-60 minutes for the same phototypes in the autumn in Europe.
- This corresponds to 6-7 minutes exposure in Miami in the summer and up to an hour in the winter
- Almost all recommendations recommend only a few minutes (10 minutes) but these are valid in a horizontal position without shade on a clear day in the summer with 25% of the body exposed.
- But in reality we live in a shaded urban environment (buildings) and spend most of the time standing (therefore only 10% of the TBSA is exposed*)
*When upright only shoulders catch the sun but the face very little: there is a difference ! Exposure is evaluated at on third if weather conditions are the same. It is one sixth for a same position if environmental factors (urban) are taken into account. 60 are minutes therefore needed.
How much time to we spend outdoors (on average) in the summer ?
- 1-2 hours.
- Therefore, in most temperate areas (such as Europe), Vitamin D levels are insufficient in the Winter (less than 45nmoles/L), Adequate in the summer (over 70nmoles/L), but suboptimal (Pearce et al. BJD 2010)
- Conclusion: Public health recommendations are therefore grossly insufficient. This is even more true if sun exposureavoidance and sunprotection are rigourously followed between periods of exposure.
Solutions ? (These are NOT recommendations)
- “two hours a day in shorts in the summer playing tennis “:
- but the overall ultraviolet (UV) would be much higher
- more exposure in an abrupt way, this is a risk factor for sunburn (solar erythema) and melanoma.
- “UVB cabin once a week from November to February and administer 1/4 of MED” (not an indoor tanning bed !)
Contributors:
Dr Christophe HSU – dermatologist. Geneva, Switzerland
Source of information: Diffey B. Sun, Vitamin D and the Skin. 19th Congress of the European Academy of Dermatology and Venereology (EADV) – Gothenburg (Göteborg), Sweden (Sverige)
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