D3 is somewhat more effective than D2 however the synthetic D2 used in vegetarian supplements, readily converts to D3 in the body and even D3 in supplements, while not technically ‘vegetarian’ is mainly derived from the oil in wool, but can also be made from lichen as a vegan source. So, even the non-vegetarian form is no ethically worse than woolly socks.
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.
Many 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. 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 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 www.vitamindtest.org.uk. 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.
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.
Alternatively, supplementing 15mcg (600ius) a day, assuming you get some from sunlight and fortified foods, should keep you close to optimum. 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 to be closer to the optimum level. 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.
However, what you’ll achieve from a vegan diet is questionable since only mushrooms that have been purposely exposed to light or UV radiation, and fortified foods, will give you any since vitamin D.
It is likely that ‘vitamin D enriched’ mushrooms will become increasingly available, which could supply 10mcg per 100g serving2. You can buy mushrooms and expose them to sunlight, or a UV lamp, and make your own. But even so it’s hard to know how much you’ll be getting.
Non-milk milks are also often fortified with vitamin D, usually giving 1.5mcg per serving. If you have one or two glasses of these, plus a serving of mushrooms, spend 30 minutes a day outdoors and supplement 15mcg you’ll be in the optimum zone.
If you spend little time outdoors and/or don't eat these kind of foods I’d recommend you supplement 25mcg a day, which is 1,000ius. This amount is also probably ideal in the winter months if you live far away from the equator. Many supplements, including drops, come in 25mcg doses. The Vegan Society recommend a supplement providing 20mcg a day.
Also, since vitamin D stores it is not necessary to take every day. Studies show that supplementing, for example, 25mcg x 7 = 175mcg, once a week is equally effective in raising blood levels.
• The only vegan food source of vitamin D is sun or UV light exposed mushrooms which should therefore state their enriched vitamin D content.
• Make a point to get outdoors for at least 30 minutes a day. The more skin you expose the more vitamin D you make.
• Supplement between 15mcg and 25mcg 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 living in the Northern or Southern hemisphere in the winter months when the angle of the sun is insufficient, and the whether not conducive, to exposing and hence making vitamin D in the skin.
My NEW book Optimum Nutrition for Vegans launched 17 December 2020! You'll find more information on my vegan web pages and you can order the book from HOLFORDirect. HOLFORDirect has launched Essentials4Vegans - a formulation I designed to support vegans with the nutrients most difficult to get on a vegan diet.
1. Bischoff-Ferrari H, ‘Optimal serum 25-hydroxyvitamin D levels for multiple health outcomes’Adv Exp Med Biol. 2014;810:500-25 DOI:10.1007/978-1-4939-0437-2_28; see also Pludowski P, et al., ‘Vitamin D supplementation guidelines’ J Steroid Biochem Mol Biol. 2018 Jan;175:125-135. doi: 10.1016/j.jsbmb.2017.01.021
2. Cardwell G, et al., ‘A Review of Mushrooms as a Potential Source of Dietary Vitamin D’ Nutrients. 2018 Oct; 10(10): 1498. doi: 10.3390/nu10101498