Your immune system doesn't run on one nutrient. Six of the ones people reach for have a documented role in keeping it working normally: vitamins A, C and D, plus iron, zinc and B12. Most of them you get from food without thinking about it. The ones worth watching on a plant-based diet are vitamin D, iron, zinc and B12.
Here is what each one does, how much you need, and where it comes from.
Vitamin D
Vitamin D contributes to the normal function of the immune system. It is also the one most of us in the UK genuinely struggle to get.
Your body makes it from direct sunlight on your skin, but between October and early March there isn't enough sunlight to do the job (1). Government advice is that everyone should consider a daily vitamin D supplement through the autumn and winter (1). Adults and children over one need 10 micrograms a day.
Food is not much help here. The main sources are oily fish and fortified foods, which thins out fast if you don't eat fish. Ours is made from lichen rather than lanolin, so it is vegan vitamin D3.
Vitamin C
Vitamin C contributes to the normal function of the immune system. It also increases iron absorption, which matters more than it sounds on a plant-based diet.
Adults aged 19 to 64 need 40mg a day (2). Oranges get the attention, but kale, broccoli, Brussels sprouts, peppers, strawberries and potatoes all carry it. Your body can't store it, so it needs topping up daily rather than loading in one go.
Vitamin A
Vitamin A contributes to the normal function of the immune system. It also has a role in normal vision and in keeping skin normal.
Men need 700 micrograms a day and women 600 (3). On a plant-based diet you get it as beta-carotene, which your body converts into vitamin A. It is what gives the colour to carrots, red peppers, spinach, mango, papaya and apricots.
Vitamin E
This is the one that turns up on immune lists without earning its place. Vitamin E's documented job is contributing to the protection of cells from oxidative stress, not immune function. Worth having. Just not for this reason.
Men need 4mg a day and women 3mg (4), and it is in plant oils, nuts, seeds and wheatgerm, so most people get enough without trying.
Iron
Iron contributes to the normal function of the immune system, to normal formation of red blood cells and haemoglobin, and to normal oxygen transport.
Men over 19 need 8.7mg a day. Women aged 19 to 49 need 14.8mg, dropping back to 8.7mg from 50 (5). The plant sources are fortified cereals, beans such as kidney and edamame, chickpeas, dried fruit, and greens like broccoli and kale. Plant iron is absorbed less readily than the iron in meat, which is where the vitamin C above earns its keep: put them in the same meal.
Zinc
Zinc contributes to the normal function of the immune system, and has a role in the process of cell division.
Men aged 19 to 64 need about 9.5mg a day and women 7mg (6). Bread, wholegrains, tofu, legumes, nuts, seeds and cereal products all carry it.
Vitamin B12
Vitamin B12 contributes to the normal function of the immune system, and to normal red blood cell formation.
It is the one nutrient on this list that plants do not provide. B12 is made by bacteria rather than by animals or plants, which is why animal foods carry it and plant foods don't. Animals get it from bacteria, often through supplemented feed. If you eat plant-based, fortified foods or a supplement are the only reliable route. Our post on the signs of a B12 deficiency covers what a shortfall looks like and how long it takes to show up.
Do You Need a Supplement?
Eat a varied diet and most of this arrives on its own. There are two real exceptions. Vitamin D is one for everyone in the UK through the winter, on government advice. B12 is one for anyone eating plant-based, every month of the year.
If you would rather cover the lot in one go, our multivitamin and minerals carries all seven of the nutrients above in a single tablet, each at 100% of your daily reference intake or more, including 14mg of iron and 50 micrograms of B12.
References
(1) https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
(2) https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-c/
(3) https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-a/
(4) https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-e/
(5) https://www.nhs.uk/conditions/vitamins-and-minerals/iron/
(6) https://www.nhs.uk/conditions/vitamins-and-minerals/others/
