Vitamin D is a fascinating chemical compound. Technically it isn’t really a vitamin but a hormone. We make it in response to sunlight but we can also get it in certain foods, although it has to be converted to its active form in the liver and then the kidneys. It’s fat-soluble, so we are able to store it, which is useful if you live in parts of the world where the sun doesn’t shine much at certain times of year.

The role of vitamin D in the body

Vitamin D helps us to absorb calcium in our gut, and keeps the balance of calcium and phosphate running smoothly. That helps our bone strength. Lack of it results in rickets in children and osteomalacia in adults, both of which are conditions where the bones become brittle and misshapen. Together with calcium it helps prevent osteoporosis. People taking aromatase inhibitors like tamoxifen are prone to osteoporosis, and vitamin D with calcium is vital in preventing it.

It also plays a part in reducing inflammation. If you’ve read my book, you’ll know inflammation is the root cause of most cancers in one way or another.

A few studies suggest that vitamin D can help prevent or manage depression (1). When sunlight is limited, some people develop Seasonal Affective Disorder (SAD) which shows up as depression. It’s thought that this is a result of a lack of serotonin, and vitamin D can affect how serotonin works.

If your vitamin D levels are low, you are likely to be more prone to respiratory infections, so it has an effect on the immune system too. A systematic review and meta-analysis of 6 randomised, placebo-controlled trials (RCTs) with 551 COVID-19 patients showed that those who took vitamin D had lower rates of hospital stays and mortality was lower too (2).

A very large RCT showed that people who took vitamin D supplements had a 22% lower rate of autoimmune conditions than those who didn’t (3). It’s clear from this and the piece of research in the previous paragraph that vitamin D helps balance the immune system.

There is also a suggestion that vitamin D can help prevent dementia. An observational study of 427,690 people showed that those with low vitamin D levels had higher rates of dementia (4). However, another review of 73 studies looking at vitamin D levels and Alzheimer’s, Parkinson’s and Multiple Sclerosis suggested that any benefits may be the result of sun exposure independent of vitamin D production (5).

Does vitamin D help prevent cancer?

We know that vitamin D helps to reduce the incidence of many different types of cancers by preventing angiogenesis (the development of blood vessels by a tumour) and helping stop tumour cells reproducing (6). Preclinical studies in animals and in vitro have also demonstrated that it helps with programmed cell death (apoptosis and autophagy), which cancer cells override (7).

Observational studies have shown an association with vitamin D deficiency (less than 30 ng/mL) and cancers of the colon, breast, ovaries and prostate (6). It has to be said that observational studies aren’t always reliable because of other possible confounding factors, and an association doesn’t necessarily mean that it causes cancer. But there is corroborating evidence: in the northern latitudes of North America, where ultraviolet B (UVB) rays are low in the long winters, cancer rates are higher (6). Also, black skins are less able to absorb UVB light, and African-Americans have vitamin D levels that are about half that of Whites, with correspondingly much higher incidences of colon, breast, ovarian and prostate cancers (6).

Not all studies agree that vitamin D supplementation reduces the risk of contracting cancers, though. In the VITAL RCT, which involved 25,871 participants, they found that vitamin D supplements didn’t have any significant effect on the number of cancer cases that were reported over around 5 years (8). However, the number of people who developed metastatic or advanced cancers was significantly lower in those people who were normal weight, although there was no reduction in those who were overweight or obese (8). This wasn’t too surprising, as it’s known that being overweight or obese affects vitamin D levels. But if you have cancer, are normal weight, and have low vitamin D levels, it would be worth improving your vitamin D levels to reduce the chances of the cancer progressing.

Another study focused on ovarian cancer and found that vitamin D prevents metastasis (9). Ovarian cancer is known as the ‘silent killer’ because it is rarely found until it metastasises. So for women it’s worth ensuring that your vitamin D levels are sufficient to ensure that, if you do develop ovarian cancer, it doesn’t spread.

So if vitamin D has anti-cancer properties, what effect does it have on skin cancers? In animal studies, vitamin D supplements reduced the growth and metastasis of skin cancers, and other studies suggest that they can protect the skin against UV damage (10). A study conducted in Finland on 500 people with a high risk of skin cancers found that those who took regular vitamin D supplements had a considerably lower risk of melanoma (11). But in a study of dietary vitamin D intake on over 100,000 people in the US, they found that there was no association with the risk of squamous cell carcinomas and melanomas, but there was a slight increase in risk of basal cell carcinomas, the most common type (10).

Given the additional protection against other cancers besides skin cancers, I believe that it’s still worth ensuring that your vitamin D levels are optimal. Just make sure that you get regular skin checks done to ensure that any skin cancers are found at an early stage. This is particularly important if you have undergone chemo or radiation therapy because they increase the likelihood of all cancers occurring, including skin cancer.

Vitamin D cancer dosage

It’s important to get your vitamin D levels tested before you start taking supplements. The sweet spot for blood levels is between 50 nmol/L (20 ng/mL) and 125 nmol/L (50 ng/mL) (12).

Aim for 800-1000 IU (20-25 micrograms) per day. Higher doses as supplements can have toxic effects.

Interactions and contraindications

Both anti-convulsants or corticosteroids can interfere with how the body processes vitamin D, so ask your health practitioner to advise on whether and how much you should use supplements.

Medicines that are bile acid sequestrants (such as cholestyramine, colestipol and colesevelam) and mineral oil can reduce absorption of vitamin D, so you may need higher doses.

Some medications can reduce the body’s vitamin D levels. If you’re taking any of the ones on the following list, it would be wise to get your levels tested:

• Isoniazid

• Rifampin

• Orlistat

• Cyclosporine

• Leflunomide

• Mycophenalate

• Mofetil

• Neomycin

• Phenobarbitol

Vitamin D increases the effects of hormone suppression drugs, so ask your health practitioner to monitor the effects closely if you are taking vitamin D supplements and adjust the dose if necessary.

Do not take vitamin D if you have sarcoidosis.

Sources of vitamin D in diet

The highest vitamin D food is cod liver oil. But not many people can stomach it because of its strong fishy taste and the tendency it has to cause fishy burps.

The next best sources of vitamin D from food are wild caught oily fish, like salmon (not farmed, which can be high in pollutants), mackerel and sardines. I don’t recommend tuna because they’re pretty large fish that eat smaller fish and can accumulate a lot of mercury and other toxins along the way.

You can buy non-dairy milk that’s fortified with vitamin D, which is the third best option after fish. I don’t recommend that you drink dairy milk. You can find out why in my book.

For those of you who choose not to eat meat, eggs are close to sardines in their vitamin D content.

Vegans are also covered: the best sources of vitamin D for vegans are mushrooms of all types. Morel, shiitake and oyster mushrooms all contain small amounts of vitamin D, but you need to eat quite a few to get anywhere near enough. Mushrooms that are exposed to UV light are able to manufacture vitamin D, so it would be worth putting mushrooms outside in sunlight for 5-10 minutes before eating them.

Because vitamin D is fat-soluble, it’s worthwhile adding some fat or oil to these foods to boost absorption before eating them. The best options are olive oil, coconut oil and butter or ghee. Avoid seed oils like canola (rapeseed), sunflower, safflower and soybean. They are high in omega 6 fatty acids, which are inflammatory, and tend to be highly processed, which can add toxic chemicals.

Vitamin D and sunlight exposure

Personally, I believe that it’s best (and cheaper) to get your vitamin D naturally from the sun. It can be quite difficult for some people to absorb vitamin D supplements and it’s hard to get sufficient from dietary sources to raise vitamin D levels to an optimal level.

We have been programmed to think that all sunlight is damaging to our skin. Sadly, as a result of the advertising around avoiding the sun, wearing hats, and using sunscreen all the time, many of us have low vitamin D levels. Statistics show that the numbers of us who are deficient in vitamin D are a staggering 24% in the US, 37% in Canada, 40% in Europe, and 23% in Australia (13, 14). Even in a group of 5 South Asian countries where the sun is strong, 68% of people were deficient (15).

Getting sunlight on your skin is contrary to everything we hear, particularly in Australia. I am not saying go out without sunscreen on in the middle of the day and sunbake. Getting sunburnt will definitely raise the risk of skin damage and skin cancers. But if you’re just exposing yourself to 5-15 minutes a day in summer early or late in the day without wearing sunscreen, you’ll be able to make sufficient vitamin D for your needs. Just don’t have so much that your skin burns. The beauty of doing it naturally is that your body controls how much you make. When you’ve had sufficient, it stops making it, so there’s no chance of overdosing.

You can find out about the pros and cons of other vitamins in my book. You can find out more here. If you’d like to buy it, click on the button below to find links to all the online places you can buy it.

References

1 Akpınar Ş, Karadağ MG. Is vitamin D important in anxiety or depression? What is the truth? Current Nutrition Reports. 2022;11(4):675-681. doi:10.1007/s13668-022-00441-0

2 Varikasuvu SR, Thangappazham B, Vykunta A, et al. Covid-19 and vitamin D (co-vivid study): A systematic review and meta-analysis of randomized controlled trials. Expert Review of Anti-infective Therapy. 2022;20(6):907-913. doi:10.1080/14787210.2022.2035217

3 Hahn J, Cook NR, Alexander EK, et al. Vitamin D and marine omega 3 fatty acid supplementation and incident autoimmune disease: Vital randomized controlled trial. BMJ. 2022;376:e066452. doi:10.1136/bmj-2021-066452

4 Navale SS, Mulugeta A, Zhou A, Llewellyn DJ, Hyppönen E. Vitamin D and brain health: An observational and Mendelian randomization study. The American Journal of Clinical Nutrition. 2022;116(2):531-540. doi:10.1093/ajcn/nqac107

5 Iacopetta K, Collins-Praino LE, Buisman-Pijlman FT, Liu J, Hutchinson AD, Hutchinson MR. Are the protective benefits of vitamin D in neurodegenerative disease dependent on route of Administration? A systematic review. Nutritional Neuroscience. 2020;23(4):251-280. doi:10.1080/1028415x.2018.1493807

6 Garland CF, Garland FC, Gorham ED, et al. The role of Vitamin D in Cancer Prevention. American Journal of Public Health. 2006;96(2):252-261. doi:10.2105/ajph.2004.045260

7 Vanhevel J, Verlinden L, Doms S, Wildiers H, Verstuyf A. The role of vitamin D in breast cancer risk and progression. Endocrine-Related Cancer. 2022;29(2):R33-R55. doi:10.1530/erc-21-0182

8 Chandler PD, Chen WY, Ajala ON, et al. Effect of vitamin D3 supplements on development of Advanced Cancer. JAMA Network Open. 2020;3(11):e2025850. doi:10.1001/jamanetworkopen.2020.25850

9 Kitami K, Yoshihara M, Tamauchi S, et al. Peritoneal restoration by repurposing vitamin D inhibits ovarian cancer dissemination via blockade of the TGF-β1/thrombospondin-1 axis. Matrix Biology. 2022;109:70-90. doi:10.1016/j.matbio.2022.03.003

10 Park SM, Li T, Wu S, Li W-Q, Qureshi AA, Cho E. Vitamin D intake and risk of skin cancer in US women and men. PLOS ONE. 2016;11(8):e0160308. doi:10.1371/journal.pone.0160308

11 University of Eastern Finland. Fewer cases of melanoma among people taking vitamin D supplements. ScienceDaily. https://www.sciencedaily.com/releases/2023/01/230109112555.htm. Published January 9, 2023. Accessed January 26, 2023.

12 Searleman E. 25-hydroxy vitamin D test: Purpose, procedure, and results. Healthline. https://www.healthline.com/health/25-hydroxy-vitamin-d-test#results. Published January 24, 2019. Accessed January 26, 2023.

13 University of Eastern Finland. Fewer cases of melanoma among people taking vitamin D supplements. ScienceDaily. https://www.sciencedaily.com/releases/2023/01/230109112555.htm. Published January 9, 2023. Accessed January 26, 2023.

14 Amrein K, Scherkl M, Hoffmann M, et al. Vitamin D deficiency 2.0: An update on the current status worldwide. Nature News. https://www.nature.com/articles/s41430-020-0558-y. Published January 20, 2020. Accessed January 26, 2023.

15 Mahbubul SH, Badhan B, Umme SR, Mohammad MR. High prevalence of vitamin D deficiency among the South Asian adults: A systematic review and meta-analysis. BMC Public Health. 2021;21(1). doi:10.1186/s12889-021-11888-1