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Sunlight & Vitamin D FAQs

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.

How do I get my vitamin D level measured and what value should I aim for?

Any doctor can order a vitamin D level check. You can also order a vitamin D test inexpensively through an online home testing company if you can’t get a check through your GP. 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).  

How much vitamin D should I be getting each day?

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.

How long do I need to be in the sun?

You need 10 to 15 minutes of all-over sun on a ‘UV index 7’ day.

You will need longer if the UV index is lower (e.g. 20 to 30 minutes if the index is 3.5) and less time in the sun if higher (e.g. 5 to 7.5 minutes if the index is 14).

Staying out longer than that won’t make any more vitamin D. Check the UV index online for your local area and time of day.

Are vitamin D megadoses safe?

Yes – taking megadoses of over 100,000 IU is perfectly safe as a once-off, 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.

Can I use a sunbed to get my vitamin D?

Sunbeds will provide vitamin D if they deliver both UVB and UVA rays, as UVB is required by the skin to manufacture vitamin D. This is an expensive way of getting adequate amounts of vitamin D compared to a spray or supplement. There is also a potential increased risk of skin cancers from prolonged sunbed use particularly as there are varying levels of regulation and strength of UV rays.

How much skin do I need to expose to get optimal vitamin D levels?

Expose as much skin as modesty and temperature allows. The more skin exposed in a 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. More information can be foudn on the website. 

Should I use sunscreen?

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.

Can I get vitamin D through glass?

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

Can I get vitamin D while swimming outdoors?

Yes. UVB penetrates water so you will be able to get vitamin D whilst swimming, provided the UV index is strong enough at the time. If the pool is indoors that will not help your vitamin D levels as UVB cannot penetrate walls nor windows.

I have been taking vitamin D3 for a few months so why are my levels are still low?

You may need a one-off megadose to get vitamin D levels up immediately if levels are initially low. It takes a while for the hormone to accumulate in fat stores (it is fat-soluble), so supplementing takes many months to raise levels. make sure you are taking the recommend 10,000 IU per day and take with your flax oil supplement to ensure you absorb it. Get your levels checked again in six months.

Can large doses of vitamin D3 cause kidney stones?

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 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 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.It was concluded that vitamin D intake above current dietary reference intakes is not associated with an increased risk of adverse events. 

Evidence from clinical trials shows that a prolonged intake of 10,000 IU/d of vitamin D3 poses no risk of adverse effects for adults.

A recent review of studies found that the incidence of stones as actually lower in those given vitamin D. In fact vitamin D is given to patients with chronic kidney disease to lower their parathyroid hormones levels, which can worsen kidney function, so it seems that their certainly isn’t any good evidence against 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.

Are vitamin D supplements safe during pregnancy?

Vitamin D is naturally occurring nutrient manufactured by skin when exposed to sunlight (UVB). It is safe to continue taking vitamin D during pregnancy (and when breast feeding), in fact it is strongly recommended for all pregnant women to take vitamin D supplements as there are many benefits for the mother and baby’s well being. It is also vital in reducing the MS risk for the child. Children of people with MS have around 30x to 40x the risk of getting MS so it is important to maintain their vitamin D levels. 

You may be tested by your doctor during your pregnancy if you are in an at risk group for vitamin D deficiency – this includes women with MS. Make sure that you check the amount of vitamin D in any prenatal vitamins you are taking, and factor this in with your vitamin D dosage.

Oral supplementation of cholecalciferol (maximum dose of 4,000 units daily) started less than 16 weeks gestation has been shown to be safe in pregnancy – Hollis BW, Johnson D, Hulsey TC, Ebeling M, Wagner CL. Vitamin D supplementation during pregnancy: double-blind, randomized clinical trial of safety and effectiveness. J Bone Miner Res. 2011;26(10):2341-57.

How can I convert ng/mL to nmol/L or vice versa?

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.

From what age should children be given vitamin D supplementation, and how much?

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.