Key questions about sunlight exposure and vitamin D supplementation are addressed here. Everything from dosage strength of vitamin D to duration of sun exposure is covered here. 

Vitamin D supplementation should start from time of conception, and continue after birth. During pregnancy, the fetus will receive adequate vitamin D from the mother, provided she is supplementing with adequate doses. To work out the appropriate vitamin D dose for your child, use the ratio of 100IU per 1kg of body weight. Provided that you follow this supplementation guideline, your child's blood levels should remain above 100nmol/L, which is felt to be the safe level to help prevent MS, and there is no need for annual blood testing.

OMS recommends that people with multiple sclerosis keep their vitamin D level at 150 -225nmol/L or 60-90ng/ml.  Those with a vitamin D level below the lower limit should consider a suitable mega-dose (this is a perfectly safe way of boosting a vitamin D level quickly). For example, if your level is 51ng/ml, then a suitable mega dose would be 100,000 IU. After the megadose, people with MS should take in 5,000-10,000 IU of vitamin D each day. This is equal to being in strong sunlight three to five times weekly for 10-15 minutes each time.

Yes - taking megadoses of over 100,000 IU is perfectly safe, and there is a comfortable margin of safety. The potential risk from particularly large doses of vitamin D is that your blood calcium levels can rise, potentially causing heart and kidney problems. However, this would only be possible with a vitamin D level of more than 400 nmol/L. To get to that level, someone would have to be taking huge doses of roughly 100,000 IU regularly.

You can use a sunbed, as long as it delivers UVB rays and not just UVA, as this is required for the skin to manufacture vitamin D. However, this would be a very expensive way of getting adequate amounts of UVB. You would also need to carefully ensure that the timing was right so that you don’t burn yourself, potentially increasing your risk of skin cancers.

Expose as much skin as modesty allows. The more you expose in a given sitting, the more vitamin D is made, but only up to a certain maximum (about 10,000 to 15,000 IU). No more is made by staying out longer, and excess exposure raises the risk of sunburn and skin cancer.

You need 10 to 15 minutes of all-over sun on a UV index 7 day. More if the UV index is lower (20 to 30 minutes if the index is 3.5) and less if the index is higher (five to seven and a half minutes if the index is 14). Staying out longer than that won’t make any more vitamin D.

Sunscreen blocks the absorption of UVB, which is responsible for vitamin D production. So, if you’re spending a short amount of time in the sun, avoid sunscreen. If you’re out for longer, it is sensible to get sun on unprotected skin for the first 10-15 minutes (depending on the UV index), and then apply sunscreen.

No. Glass filters out UVB (the wavelength required to make vitamin D).

Yes. UVB penetrates water so you will be able to get vitamin D whilst swimming. If the pool is indoors, however, even under a skylight, that will not help your vitamin D levels. UVB penetrates neither walls nor windows.

Any doctor can order a vitamin D level check. For people with MS, OMS recommends keeping around 150 nmol/L (60 ng/mL). In the tropics, where there are lower levels of MS (because of the abundant sunshine), people often have levels in the region of 200-220 nmol/L (80-88 ng/mL).

Everyone needs a one-off megadose to get vitamin D levels up immediately if levels are initially low, as they usually are. It takes ages for the hormone to accumulate in fat stores (it is fat-soluble), so supplementing takes many, many months to raise levels. Get your levels checked again in six months.

There is very little clinical trial evidence to support this claim. The Women's Health Initiative study reported a small increase in kidney stones in postmenopausal women aged 50 to 79 years whose daily vitamin D3 intake was 400 IU (the reference intake for 50 to 70 years, and below the reference intake for >70 years) combined with 1,000 mg calcium.

The increase in renal stones corresponded to 5.7 events per 10,000 person-years of exposure. The women in this trial had higher calcium intakes than is seen in most post-menopausal women.

But it is so difficult in this study to determine the effect of vitamin D because the supplements were so small, and they don't provide details of the vitamin D levels of those who got stones and those who didn't.

It is not possible to reach any conclusions about risk of kidney stones with vitamin D supplements from this paper.

In another paper  that reviews the literature and references the WHI trial, the conclusion is reached that high calcium intake probably caused the effect of kidney stones seen in the trial.

There is little evidence from any trials that vitamin D above current reference intakes is harmful. In most trials, reports of hypercalcemia and hypercalciuria were not associated with clinically relevant events.

It was concluded that vitamin D intake above current dietary reference intakes is not associated with an increased risk of adverse events. A good review of what constitutes a safe dose of vitamin D was published in 2009.

Evidence from clinical trials shows, with a wide margin of confidence, that a prolonged intake of 10,000 IU/d of vitamin D3 poses no risk of adverse effects for adults, even if this is added to a rather high physiologic background level of vitamin D.


  1. Rebecca D. Jackson, M.D., Andrea Z. LaCroix, Ph.D., et al. Calcium plus Vitamin D Supplementation and the Risk of Fractures. NEJM 354(7):669-683 February 16, 2006.
  2. Cranney A, Horsley T, et al. Effectiveness and safety of vitamin D in relation to bone health. Evid Rep. Technol Assess (Full Rep). 2007 Aug:(158):1-235.
  3. Vieth R. Vitamin D and cancer mini-symposium: the risk of additional vitamin D. Ann Epidemiol. 2009 Jul;19(7):441-5. Epub 2009 Apr 11.

The important thing about this question is more about the risk of the child developing MS as an adult, and much less about the mother's health, because pregnancy is very protective for the mother. As you know, children of people with MS have around 30x to 40x the risk of getting MS as others in the population. That is a very high risk. Vitamin D supplementation during pregnancy is recommended to lower that risk. In my view, the evidence now is very clear that vitamin D supplementation lowers the risk of getting MS throughout life. This has been shown in a number of studies, including the Nurses Health Study. The evidence base around supplementation in utero is growing rapidly. There has been much published about the risks of developing MS related to season of birth. One paper on this was published in Melbourne, from the Murdoch Children’s Research Institute, from Anne-Louise Ponsonby's group. Click here for the link to the full paper. Their last paragraph sums up the situation well:

"The findings here provide the first population based evidence beyond month of birth patterns to indicate that vitamin D supplementation for the prevention of multiple sclerosis might also need to be considered during in utero development."

Chaudhuri, a Glasgow neurologist, was probably the first to strongly advocate this in 2005: Med Hypotheses. 2005;64(3):608-18.

Why we should offer routine vitamin D supplementation in pregnancy and childhood to prevent multiple sclerosis.

Chaudhuri A. Department of Neurology, Institute of Neurological Sciences, 1345 Govan Road, Glasgow G51 4TF, Abstract

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that runs a chronic course and disables young people. The disease is more prevalent in the geographic areas that are farthest from the equator.

No form of treatment is known to be effective in preventing MS or its disabling complications. A number of epidemiological studies have shown a protective effect of exposure to sunlight during early life and a recent longitudinal study confirmed that vitamin D supplementation reduced life-time prevalence of MS in women.

Very little is known regarding the role of vitamin D on the developing brain but experimental data suggest that cerebral white matter is vitamin D responsive and oligodendrocytes in the brain and spinal cord and express vitamin D receptors.

It is possible that differentiation and axonal adhesion of oligodendrocytes are influenced by vitamin D level during brain development and a relative lack of vitamin D may increase oligodendroglial apoptosis.

The age effect of migration on susceptibility to develop MS could be explained by a role of vitamin D on brain development. In areas of high MS prevalence, dietary supplementation of vitamin D in early life may reduce the incidence of MS.

In addition, like folic acid, vitamin D supplementation should also be routinely recommended in pregnancy.

Prevention of MS by modifying an important environmental factor (sunlight exposure and vitamin D level) offers a practical and cost-effective way to reduce the burden of the disease in the future generations.

In my view, the only question is what dose of vitamin D one should take. Many neurologists are not really familiar with dosages for vitamin D supplementation, as they do not use this in any of the other neurological diseases they manage.

There is also a widespread irrational fear in medicine about overdosage of this naturally occurring hormone.

Consider this: if you step outside in any warm city in summertime with only a bathing suit on for around five minutes at midday, you will make 15,000 IU of vitamin D immediately. Why would you be told not to take 1,000 IU? How could that be toxic?

This is probably one of the few papers that really make a recommendation about doses during pregnancy. Hollis is one of the world experts on vitamin D.

He has published 202 papers on vitamin D in the world's best journals.

The current recommended dietary requirement for vitamin D intake (200 IU/d) during pregnancy and lactation is based on little, if any, scientific evidence, and as a result is clinically irrelevant with respect to maintaining nutritional vitamin D status during these demanding human conditions.

Current research has shown that the actual dietary requirement during pregnancy and lactation may actually be as high as 6,000 IU/d. Current data on which these new recommendations could be based are presented.

In the US, the measure used is ng/mL, with 40ng/mL equivalent to about 100nmol/L. So, if your reading in the US is ng/mL, multiply by 2.5 to get the nmol/L we discuss on this site. For example:

  • For a reading of 50ng/mL in the US, multiply by 2.5 and the reading for elsewhere in the world will be 125nmol/L
  • For a reading of 125nmol/L elsewhere in the world, divide by 2.5 and the US reading will be 50ng/mL.

Vitamin D levels in the body can be easily measured with a simple blood test. Until fairly recently, a level of less than 25nmol/L was considered to represent moderate to severe deficiency, and a level of 25-50nmol/L meant mild deficiency. Many laboratories have now changed their recommended normal levels to 75-250nmol/L, reflecting recent research that indicates a higher upper level of normal is quite safe. So, currently <75nmol/L is considered insufficient, and <50nmol/L is deficient.