A recent animal study from the University of Wisconsin has given a new perspective on the role of vitamin D and sunlight in the development of multiple sclerosis (MS).
It is well established that MS is more common further away from the equator in both hemispheres. This has generally been attributed to lack of vitamin D production due to lack of sunlight, but there is increasing awareness that sunlight itself may be positively affecting the immune system independent of vitamin D, in a way that may decrease the risk of MS.
In several recent studies, ultraviolet (UV) radiation has been found to suppress an animal model of MS, independent of vitamin D production. For instance, in some animal models, UV suppresses MS even in an animal state of vitamin D deficiency. And in further models, UV suppresses MS even when vitamin D receptors are removed from the animal.
In the present animal model study, the researchers wanted to see just which wavelength of UV radiation is responsible for the effect seen in the above-mentioned studies. UV radiation is classified by wavelength. Here are the wavelengths used in this study and some additional wavelengths:
- UVC: 100-280 nm. This range is completely blocked by the ozone layer.
- Broad band (BB) UVB: 280-320 nm. This range helps you produce vitamin D in the skin and also induces sunburn with overexposure.
- Narrow band (NB) UVB: 300-315 nm. This range helps you produce vitamin D but doesn’t include some of the more harmful rays in the 280-300 nm range. Still, you can definitely burn with overexposure in this range.
- Broad band (BB) UVA: 300-400 nm.
- UVA-1: 340-400 nm.
Both forms of UVA penetrate deeply into the skin and cause the formation of free radicals. In small doses, these UV radiations safely and successfully treat inflammatory skin diseases like psoriasis and eczema. UVA doesn’t help you produce vitamin D. You can also burn with UVA, although it isn’t as intense as UVB.
In this study, the researchers induced an MS-like state in mice and then divided them into groups based on type of UV exposure:
- BB UVB
- NB UVB
- BB UVA
- UVA 1
The mice received UV exposures according to their group for seven days before and 30 days after the induction of neurological disease. Blood samples were taken to determine serum vitamin D and calcium levels. Only mice in the BB UVB group had a statistically significant increase in their vitamin D levels. None of the mice had a significant change in their serum calcium levels.
Neurological disease was significantly suppressed in the mice receiving the BB and NB UVB radiation, suggesting that UV light in the 300-315 nm wavelength range is largely responsible for the effect. This effect was dose-dependent, meaning the more UV exposure the mice received, the less neurological symptoms they had.
BB UVA had a mildly positive effect at a low dose and a moderate effect at a higher dose. UVA-1 radiation did not successfully treat the mice at any dose. The positive effects of the BB UVA are likely due to the overlap of this spectrum with the wavelengths in the NB UVB range.
The researchers concluded that UV radiation between 280 and 340 nm effectively treats an animal model of MS, with the “effectiveness…largely captured by a narrow band of UV light between 300 and 315 nm with a peak at 311 nm.” Since only the BB UVB group saw a significant increase in vitamin D levels, yet the NB UVB group also experienced an equal suppression of the MS-model, the researchers concluded that the 300 to 315 nm range of UV light suppressed the MS-model independent of vitamin D. They note, “These findings force a reexamination of the idea that vitamin D production mediates the relationship between UV light and MS.”
An additional benefit of using NB UVB light is that it is less likely to cause a sunburn than BB UVB exposure. The researchers hypothesized that UV radiation might be converting some “unknown compound” in the skin into a substance that protects against MS, or that the light is affecting the immune system in some other positive way. They concluded that it is reasonable to assume that humans are positively affected in a manner similar to the mice, and urged for trials of NB UVB radiation in people with MS.
While the majority of the vitamin D community believes it is wise to maintain a vitamin D level between 40 and 60 ng/mL, research is increasingly finding benefits to UV light exposure above and beyond vitamin D production. Our ancestors evolved in sun-drenched, equatorial Africa. Safe and sensible sun exposure is therefore likely a critical component of our overall health and well-being.