Vitamin D – supplements or sunshine?
Many doctors now recommend that people with multiple sclerosis take vitamin D supplements. However, recent studies have suggested that it may not have much impact on MS – and may not be as good as a little sun exposure.
Vitamin D is the “sunshine vitamin” because it is produced by the body from sun exposure. Ultraviolet radiation (UV-B) converts a substance in the skin to cholecalciferol, a pre-vitamin that travels to the liver and kidneys to be converted to a form of vitamin D that the body can use (called calcitriol). The amount of vitamin D that’s produced will depend on the intensity of the sunlight (which varies depending on time of day and latitude) and skin colour (lighter skin produces more vitamin D than darker skin). The recommended daily allowance of vitamin D is 600 IU with a maximum of 4000 IU/day (https://ods.od.nih.gov/factsheets/vitamind-HealthProfessional/).
Under ideal conditions, the skin can produce about 20,000 IU of vitamin D after 30 minutes of sun exposure – more than enough to meet your body’s needs. Vitamin D can also be obtained with consumption of fish (salmon, mackerel), egg yolks and vitamin-fortified foods (such as milk and orange juice).
Vitamin D supplements have become popular because many people in northern countries are deficient in vitamin D. Two factors are largely to blame: there is insufficient sunlight during the winter months, and people tend to spend much of their time indoors or use sun screens to block the UV rays needed for vitamin D.
The MS-vitamin D connection began with two observations: MS is more common in northern latitudes, where sunlight is less intense than at the equator; and people living near the sea, who typically eat more fish, are less likely to develop MS. Sunlight and diet appear to compensate each other: among people living in the Arctic Circle, consumption of fish (including cod liver oil) provided enough vitamin D to offset the deficit from minimal sun exposure (Kampman and colleagues. J Neurol 2007;254:471-477).
These observations led to studies which showed that that people with higher vitamin D levels in their blood stream were less likely to develop MS (Lucas and colleagues. Neurology 2011;76:540-548). There were also reports that vitamin D supplements, when taken with an MS drug such as one of the interferons or Tysabri, could reduce the severity of MS (Soilu-Hanninen and colleagues. J Neurol Neurosurg Psychiatry 2012;83:565-571. Laursen and colleagues. Mult Scler Relat Disord 2016;10:169-173).
That said, there were also many studies that found that vitamin D had little impact on MS. A recent analysis of 12 studies concluded that vitamin D supplements have no effect on MS relapses, worsening disability or MS lesions in the brain (Jagannath and colleagues. Cochrane Database Syst Rev 2018;9:CD008422). Indeed, very high doses of vitamin D may be harmful because it increases the body’s ability to absorb calcium. In animal studies of MS, this increase in calcium due to high-dose vitamin D actually worsened the level of inflammation in the brain (Hausler and colleagues. Brain 2019; epublished July 13, 2019).
Which brings us back to sunlight. Sunlight and supplements are similar in that both raise the level of vitamin D in the blood stream. But similar is not the same. Sun exposure also produces another substance in the skin (called urocanic acid, or UCA), which has been shown to suppress the immune response (Gibbs and colleagues. Photochem Photobiol Sci 2008;7:655-667). UCA levels in the blood stream are also low in people with MS. This has led some researchers to question whether the problem of low sun exposure is a matter of UCA deficiency rather than vitamin D deficiency (Hausler and colleagues. Int J Mol Sci 2019;20:218).
In recent years, sun exposure has been equated with melanoma (a form of skin cancer) but that public opinion pendulum away from sunshine may be shifting back. While getting a sunburn can double the risk of melanoma (Gandini and colleagues. Eur J Cancer 2005;41:45-60), non-burning sun exposure actually reduces the risk of melanoma (Moan and colleagues. Proc Natl Acad Sci USA 2008;105:668-673). Non-burning sun exposure has also been shown to reduce the risk of breast cancer, liver disease, autoimmune disorders and other conditions – including multiple sclerosis (Baarnhielm and colleagues. Eur J Neuro 2012;19:955-962). Conversely, too little sun exposure has been linked to hypertension, heart disease, diabetes and obesity. This has led one group of experts to state: “Insufficient sun exposure has become a major public health problem, demanding an immediate change in the current sun-avoidance public health advice” (Hoel and colleagues. Dermatoendocrinol 2016;8:e1248325).
The key, as in all things, is moderation. One recommendation is for Caucasians living in northern countries to spend 15 minutes a day in the sun with their face, arms and legs exposed (half that time if sporting a bathing suit) for 2-3 days of the week (Hoel 2016). People with darker skin would benefit from somewhat longer sun exposure. And greater sun exposure is also recommended for everyone during the winter months that will be soon upon us.
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