Are You Getting Enough Vitamin D?

There are two forms of vitamin D – vitamin D2 is made in plants, notably mushrooms, while D3 is found in animal produce, with fish being the richest source, and is also produced in the skin. Our main source of vitamin D is from sunlight acting on the skin. But you need to expose your arms and face for at least half an hour a day to make reasonable amounts. In fact, the vitamin D in mushrooms is made by exposing them to light, which then converts plant sterols into vitamin D.

D3 is somewhat more effective than D2 however the synthetic D2 used in vegetarian supplements does ultimately converts to D3 in the body and even D3 in supplements, while not technically ‘vegetarian’ are mainly derived from the oil in wool. Vitamin D3 is also found in lichen, which is therefore a vegan source of this preferable form.

Whatever the source of vitamin D is has to convert into 25-hydroxyvitamin D, which acts more like a hormone than a vitamin. It used to be thought that vitamin D’s only role was to ‘fix’ calcium into bone, hence deficiency results in rickets in children and osteoporosis in older adults. But, in the last twenty years it’s become clear that vitamin D has many other roles in the body, including controlling cell growth and inhibiting growth of cancer cells, boosting immunity, strengthening muscles and reducing of inflammation. It also influences over 200 genes. It may also be helpful for preventing depression, especially in the winter, reducing infections, as well as the risk for numerous disease including diabetes, heart disease and cancer, but also multiple sclerosis and other auto-immune and neurological diseases such as dementia and Parkinson’s. In short, it’s a no-brainer to keep your vitamin D level close to optimal.

Most people, especially vegans, don’t get enough vitamin D, so much so that it is now recognised that everyone living in the far Northern (and Southern) hemisphere, where the angle of the sun in the winter is insufficient to make much vitamin D, and the cold climate not conducive to exposing naked skin to sunlight, need to supplement this versatile vitamin from October to March. On the other hand, if you live in sunnier climes and spend lots of time outdoors, you may just make enough just from the synthesis of vitamin D, acting on cholesterol in the skin. Vitamin D also stores so if you spend a couple of weeks in the sun in the winter months that too might see you through.

Due to these variables it is ideal to know your vitamin D status by measuring your blood level of 25-hydroxyvitamin D. The level you’re shooting for is at least 75 nmol/l. Below 50nmol/l is considered inadequate. Fortunately, this is one inexpensive test many GPs are willing to measure. If not, you can get relatively inexpensive home test kits (£29) online from If your level is low it’s best to supplement 25mcg a day (1,000ius) and recheck that you’ve achieved a level of 75nmol/l or more. it may even be preferable to get your level up to 100nmol/l, which is what peopel who live closer to the Equator achieve. This may offer even greater protection against infections in the winter since vitamin D is vital for immune function.

How much do you need to take in to get your blood level up to 75 nmol/l? A review of studies concludes that an intake of 20mcg (800iu) of vitamin D per day for all adults may bring 97% of the population to level of at least 50 nmol/l and about 50% up to 75 nmol/l. This level both optimises disease prevention and bone health1.

I used to think that supplementing 15mcg (600ius) a day, assuming you get some from sunlight and fortified foods, should keep you close to optimum.  This may be enough in the summer but it certainly isn’t enough in the winter months. The RDA in the UK used to be 5mcg but the EU and US recommended intake has been increased to 15mcg a day. I consider a total intake of 30mcg (1,250ius) to be closer to the optimum level in the summer if you spend at least 20 minutes outdoors in shorts and t-shirt. You only make significant amounts of vitamin D when your shadow is no longer than your body, as a rough guide. Thirty minutes of sun exposure a day may provide you with the equivalent of 10mcg. Those eating fish and eggs may achieve a further 5mcg.

In the winter you’ll probably need 1,600iu to 2000iu (40-50µg) vitamin D3 needed to achieve at least 75nmol/l. This is also what you need for optimal disease prevention. For optimal immune function, for example during winter flu season, you’d be wise to supplement a bit more, 3,000iu a day.

Since vitamin D stores in the body, and takes several days to convert into the stored form, taking a weekly dose ie 7 x 3,000iu = 21,000iu a week, is just as effective.

Your Quick Guide to Vitamin D

Make a point of getting outdoors for at least 30 minutes a day. The more skin you expose to the sun, the more skin you expose to the sun, the more vitamin D you will make.

Supplement between 15mcg (600 iu) and 25mcg (3,000 iu) of vitamin D, the higher level being more suitable either in the winter or for those who do not get daily sun exposure, and for all those living in the far northern or far southern hemisphere in the winter months when the angle of the sun is insufficient, and the wather is not conducive to exposing the skin, and hence making vitamin D in the skin.

HOLFORDirect stock my NEW unique Vitamin D3 formula, which is high strength (3000iu) formulated by me based on the most up -to-date research and I’ve also made it suitable for vegans.

Vitamin D testing is usually available through your doctor. Alternatively, you can be tested for £29, using a home test kit for blood collection, which is then sent back to the laboratory. See It is also part of York’s Essential Health Check. Use the code PH10 to get 10% discount.

Vitamin D and VIRUSES

As the evidence grows for the importance of vitamin D in aiding protection against viruses, including COVID-19, the campaign for increased Vitamin D use is gaining momentum. In recent weeks over 300 professors, doctors and scientists have written to Governments and medical authorities to encourage recommended daily Vitamin D intake in relation to COVID-19 – Collectively, these experts recommend between 2,000 and 4,000iu a day of D3, the most potent form of Vitamin D, based on the evidence. Read my Blog. 


On Friday 12 February, I’m going to be talking to my ‘go to’ guy for anything to do with vitamin D. For more years, or decades than I care to remember, Dr William Grant has been the ultimate vitamin D ferret, squirreling away all the studies, digging deeply into the mechanisms, and working closely with the Grassroots health initiative, which we’ll talk about, and the ‘informant’ for ultimate digital resource.

William Grant is the Founder and Director of Sunlight, Nutrition and Health Research Center, San Francisco. This is a non-profit organization devoted to research and education regarding diet, UVB exposure and vitamin D for reduced risk of chronic and infectious diseases.

Listen to my podcast – available from 7pm on Friday 12 February 2021.