Vitamin D - the cheap life insurance

Note: This article was originally written in 2007 and although it has been updated in 2010, the research can still be somewhat outdated. For more information see the website of Vitamin D Council.

Vitamin D is best known for its importance in maintaining bone strength, but it has a variety of functions in the body. It is particularly important for the immune system, in the prevention autoimmunity and cancer. The skin can produce vitamin D in sufficient sunlight and some foods also contain it, either naturally or through fortification, but for many people supplementation is still required.

Current recommendations of vitamin D intake are considered to be way too low by the leading vitamin D researchers. Usually the recommendation is 200-800 IU or 5-20 mcg (micrograms, one millionth of a gram) a day, while most vitamin D researchers recommend at least 100 mcg a day.

Margarine and milk (and sometimes cereal) are fortified in many countries, but the amounts are inadequate. Eggs are another source, but you'd need to eat dozens of eggs a day. The only significant food sources of vitamin D are some wild mushrooms and fish, but even eating them daily it is difficult to get anywhere near the amounts one gets from the sun.

Just 20 minutes in sunlight is enough for most light-skinned persons to produce 250 mcg (10,000 IU) of vitamin D, which shows how insufficient the current recommendations really are and how non-toxic vitamin D really is. So why isn't sunlight enough? Because in many countries sunlight only produces vitamin D for a part of the year, sometimes only for a few months. Even in the summertime covering your skin with clothes or sunscreen greatly reduces the rate of vitamin D production.

People with a dark skin produce vitamin D at a much slower rate, so especially those black people who live in the north are at significant risk, and studies show that they are usually deficient in vitamin D. However, according to studies even some light-skinned people that get plenty of sun exposure are often deficient, which likely means that some people don't produce vitamin D as effectively as others.

So what are the benefits of supplementing with vitamin D?

  • It reduces the risk of cancer.[1]
  • It reduces the risk of cardiovascular disease.[2]
  • It reduces the risk of multiple sclerosis[3],[4] and likely other autoimmune diseases[5],[6] as well.
  • It reduces the risk of osteoporosis.[7]
  • It reduces the risk of catching influenza and other respiratory infections.[8]
  • It reduces the risk of both type I[9] diabetes and likely type II as well.[10]
  • It appears to be be neuroprotective [11] and slow down physical and cognitive aging.[12],[13]
  • It may reduce the risk of schizophrenia[14] and may have a role in regulating mood.[12],[15]

Vitamin D deficiency has been suspected of being the cause or one of the causes of seasonal depression (SAD). It has been implicated in autism as well (specifically a vitamin D deficiency of pregnant mothers), but there are no studies examining this theory yet, so we have to take it as a compelling hypothesis for the time being. Autism has been suspected to be an autoimmune disorder and it is known to have immune components.

The first study there is a review of over 50 different studies looking at vitamin D and cancer risk. There are also many studies that show that sunlight reduces cancer incidence and/or mortality. That doesn't prove that vitamin D is the factor behind this observation, but considering that there are many studies showing the inverse association between cancer and high vitamin D intake and/or blood levels it seems very likely.

Vitamin D has been associated with a lowered risk of at least the following cancers: prostate, breast, stomach, colorectal, liver, gallbladder, pancreas, lung, bladder and kidney. The association is particularly strong with colon, breast and prostate cancers - the latter two being the most common cancers (excluding the very benign forms of skin cancer that are normally not included in cancer statistics) in women and men, respectively. Cancer of the pancreas can occur in people in their 30s and sometimes even in their 20s and it currently has an extremely high mortality, more than 95%. Lung cancer is more an illness of older people (not exclusively of smokers!), but it also comes with a pretty grim prognosis. Only about 10-15% of patients survive for more than five years.

If you think that the reductions in risk are small and insignificant, think again. Some studies have shown that supplementation may reduce cancer risk by up to 60% - which isn't anything to shrug off, considering that one in three people is estimated to get cancer in their lifetime. Getting inadequate amounts of vitamin D is a health hazard similar to smoking or obesity. And if you do smoke and don't get enough vitamin D, you have two serious risk factors already - and even more if you're significantly overweight. Quitting smoking and losing weight is easier said than done for many people, but luckily supplementing with vitamin D is very easy and inexpensive.

Vitamin D may also be useful in the prevention and treatment of various other illnesses and conditions, such as stroke, osteoarthritis, COPD, epilepsy, PMS, PCOS (polycystic ovaries), migraine, periodontal disease, asthma, allergies, CFS/ME, fibromyalgia, benign prostate hyperplasia and Parkinson's disease.

So, how should I acquire my vitamin D?

You should try to get 20 minutes of sun exposure three times a week in the summer, while not wearing sunscreen or having most of your body covered in clothes (you can apply sunscreen after that if needed). Longer periods of sunbathing do not provide additional benefit, as after the rate of vitamin D being produced is no bigger than the amount of it being destroyed. Of course, if you have any medical reasons that prevent you from being in the sun (such as lupus or photosensitizing medication) you should not take this advice, but supplement with vitamin D instead.

In the winter everyone should get at least 100 mcg of vitamin D a day. Unless you eat wild mushrooms and/or fatty fish almost every day, you'll most likely need to supplement with vitamin D in pill or liquid form. Try to choose a source that says it contains vitamin D3, as this form of vitamin D is more effectively absorbed than D2. Supplementation (with a smaller amount) during the summer is also a good idea, since you might be one of the folks who don't produce enough vitamin D even given sunlight.

Do not take cod liver oil to get your vitamin D! The reason for this is that cod liver oil, like all liver products, contains massive quantities of vitamin A. While vitamin A is of course important as well, hardly anyone in the Western world eating even remotely normally is deficient in it. If you take enough cod liver oil to get an ample dose of vitamin D, you can get vitamin A poisoning. And unlike with most vitamins, even doses slightly larger than the RDA can be harmful. Taking too much vitamin A can adversely affect your bone strength.

How do I know I have enough of vitamin D/How do I know I'm not taking too much?

The best way to know if you have adequate levels of vitamin D is to have it tested with a blood test. This is an important test, but most doctors rarely ever consider it. It costs about $50 if you have to pay for it out of pocket.

However, even if you don't have it tested, it is completely safe to take these doses, as the human body can produce up to 250 mcg (10,000 IU) in just 20 minutes.The reason for having a blood test isn't the risk of getting excessively high levels, but many people need as much as 150-250 mcg a day (or even more!) to reach healthy blood levels.

Does vitamin D supplementation help if I already have one of those diseases? Can it help in other conditions?

There isn't clear evidence for all of these conditions, but for many it seems to. And even if you have one of those diseases, you can still get another one (e.g. if you have multiple sclerosis you can still get cancer - and may be even more likely to get cancer). According to one study the administration of vitamin D reduces the disease progression in an animal model of multiple sclerosis.[16] Vitamin D seems to be an effective treatment for prostate cancer.[17] There is some evidence that it might work for colorectal cancer as well.[18]

While you can't prevent HIV infection with vitamin D (or even if you can, condoms and other measures are a much more important way), it seems like supplementing with vitamin D is probably a good idea in HIV/AIDS as well.[19]

Since sunlight makes the body produce vitamin D, does solarium have the same effect?

Vitamin D production requires UVB rays. Some solarium equipment only produces UVA spectrum rays, which doesn't promote production of vitamin D. So, it depends entirely on your solarium (I assume this is written on the actual machine, or the papers that come with the solarium have the information). I'd still recommend supplementation instead of using solarium during the winter. But if you're going to frequently use a solarium that produces UVB radiation for other reasons anyway, you can probably reduce the amount you're supplementing, but it's not necessary.

Other ways to reduce the risk of cancer or other illnesses

Of course, vitamin D supplementation isn't the only way to reduce cancer risk. If you smoke, quitting smoking is the best thing you can do - but you certainly knew that already. Consuming large quantities of alcohol is a cancer risk - and not just for liver cancer. Even lung cancer risk goes up with alcohol use, and so do the risks of e.g. breast and colorectal cancer.[20] Exercise, besides being healthy in general, can reduce the risk of e.g. breast cancer. If you're obese, losing weight is a good way to lower your risk of some cancers, e.g. one of the very deadliest, the pancreatic cancer.[21]

There is another fairly easy way too - supplementing with selenium. It appears to decrease the risk of several cancers and slow down the spread of already existing tumors.[22],[23] It probably isn't as good as vitamin D for reducing the risk of cancer and other illnesses, but as it is an antoxidant and beneficial to the immune system it may also prevent other conditions and/or reduce the damage they cause, particularly viral infections and cardiovascular disease.[24]

The drug low dose naltrexone (LDN) has been used in the treatment of autoimmune and neurological illnesses, HIV/AIDS, cancer and many other conditions. Some people also use it as a cancer preventative. There is no evidence of its efficacy in this use, but lab studies support the mode of action in cancer prevention.


[1] Garland CF, Garland FC, Gorham ED et al. The role of vitamin D in cancer prevention. Am J Public Health. 2006 Feb;96(2):252-61. PMID: 16380576

[2] Martins D, Wolf M, Pan D et al. Prevalence of cardiovascular risk factors and the serum levels of 25-hydroxyvitamin D in the United States: data from the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2007 Jun 11;167(11):1159-65. PMID: 17563024

[3] Hayes CE, Cantorna MT, DeLuca HF. Vitamin D and multiple sclerosis. Proc Soc Exp Biol Med. 1997 Oct;216(1):21-7. PMID: 9316607

[4] VanAmerongen BM, Dijkstra CD, Lips P. Multiple sclerosis and vitamin D: an update. Eur J Clin Nutr. 2004 Aug;58(8):1095-109. PMID: 15054436

[5] Ginanjar E, Sumariyono , Setiati S et al. Vitamin d and autoimmune disease. Acta Med Indones. 2007 Oct-Dec;39(3):133-41. PMID: 17699936

[6] Arnson Y, Amital H, Shoenfeld Y et al. Vitamin D and autoimmunity: new aetiological and therapeutic considerations. Ann Rheum Dis. 2007 Sep;66(9):1137-42. PMID: 7557889

[7] Holick MF. The role of vitamin D for bone health and fracture prevention. Curr Osteoporos Rep. 2006 Sep;4(3):96-102. PMID: 16907998

[8] Cannell JJ, Vieth R, Umhau JC et al. Epidemic influenza and vitamin D. Epidemiol Infect. 2006 Dec;134(6):1129-40. PMID: 16959053

[9] Hyppönen E, Läärä E, Reunanen A et al. Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study. Lancet. 2001 Nov 3;358(9292):1500-3. PMID: 11705562

[10] Pittas AG, Lau J, Hu FB et al. The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis. J Clin Endocrinol Metab. 2007 Jun;92(6):2017-29. PMID: 17389701

[11] Brewer LD, Thibault V, Chen KC et al. Vitamin D hormone confers neuroprotection in parallel with downregulation of L-type calcium channel expression in hippocampal neurons. J Neurosci. 2001 Jan 1;21(1):98-108. PMID: 11150325

[12] Wilkins CH, Sheline YI, Roe CM et al. Vitamin D deficiency is associated with low mood and worse cognitive performance in older adults. Am J Geriatr Psychiatry. 2006 Dec;14(12):1032-40. PMID: 17138809

[13] Wicherts IS, van Schoor NM, Boeke AJ et al. Vitamin D status predicts physical performance and its decline in older persons. J Clin Endocrinol Metab. 2007 Jun;92(6):2058-65. PMID: 17341569

[14] McGrath J, Saari K, Hakko H. Vitamin D supplementation during the first year of life and risk of schizophrenia: a Finnish birth cohort study. Schizophr Res. 2004 Apr 1;67(2-3):237-45. PMID: 14984883

[15] Berk M, Sanders KM, Pasco JA et al. Vitamin D deficiency may play a role in depression. Med Hypotheses. 2007 May 10. PMID: 17499448

[16] Cantorna MT, Hayes CE, DeLuca HF. 1,25-Dihydroxyvitamin D3 reversibly blocks the progression of relapsing encephalomyelitis, a model of multiple sclerosis. Proc Natl Acad Sci U S A. 1996 Jul 23;93(15):7861-4. PMID: 8755567

[17] Schwartz GG, Oeler TA, Uskokovic MR et al. Human prostate cancer cells: inhibition of proliferation by vitamin D analogs. Anticancer Res. 1994 May-Jun;14(3A):1077-81. PMID: 8074453

[18] Niv Y, Sperber AD, Figer A et al. In colorectal carcinoma patients, serum vitamin D levels vary according to stage of the carcinoma. Cancer. 1999 Aug 1;86(3):391-7. PMID: 10430245

[19] Haug CJ, Aukrust P, Haug E et al. Severe deficiency of 1,25-dihydroxyvitamin D3 in human immunodeficiency virus infection: association with immunological hyperactivity and only minor changes in calcium homeostasis. J Clin Endocrinol Metab. 1998 Nov;83(11):3832-8. PMID: 9814454

[20] Seitz HK, Becker P. Alcohol metabolism and cancer risk. Alcohol Res Health. 2007;30(1):38-41, 44-7. PMID: 17718399

[21] Lin Y, Kikuchi S, Tamakoshi A et al. Obesity, physical activity and the risk of pancreatic cancer in a large Japanese cohort. Int J Cancer. 2007 Jun 15;120(12):2665-71. PMID: 17304505

[22] Zeng H, Combs GF Jr. Selenium as an anticancer nutrient: roles in cell proliferation and tumor cell invasion. J Nutr Biochem. 2007 Jun 22. PMID: 17588734

[23] Piekutowski K, Makarewicz R, Zachara BA. The antioxidative role of selenium in pathogenesis of cancer of the female reproductive system. Neoplasma. 2007;54(5):374-8. PMID: 17688366

[24] Rayman MP, Rayman MP. The argument for increasing selenium intake. Proc Nutr Soc. 2002 May;61(2):203-15. PMID: 12133202

Disclaimer: This article is written by me (Maija Haavisto). It only provides links to a small fraction of the research done on the subject, as I don't have infinite resources. I am not a medical professional and I take no responsibility of any other possible errors in this information. Medicine is a constantly evolving science. This information is not intended to treat, cure or diagnose any illness. You use it at your own risk. If you are worried you are suffering from a chronic illness or may be at an increased risk for getting one, you should discuss it with your doctor. However, don't assume your doctor knows anything about vitamin D. Most doctors have very little information about nutrition and the little they have is outdated. Sadly, only a small minority of doctors follow scientific research - according to a study I'm unable to locate right now as few as five per cent.