24 May 2023 Article

Vitamin D (cholecalciferol) is needed for the optimal absorption of dietary calcium. It is therefore important for the growth and maintenance of strong bones and teeth. In addition, vitamin D plays a role in the proper functioning of the muscles and the immune system.

The sun vitamin

Sunlight is the main source of vitamin D. The human body can produce vitamin D itself under the influence of sunlight in the skin. Vitamin D is also found in some animal foods, specifically in oily fish, and in lower levels in meat, eggs and butter. Vegetarians and especially vegans get very little to zero vitamin D from food sources.

In the spring, summer and autumn, the advice regarding vitamin D is to spend at least 15 to 30 minutes between 11 a.m. and 3 p.m. with your head and hands uncovered in the sun every day. When a larger part of the body is exposed, a shorter time is sufficient. Your body then produces vitamin D and stores it. In the winter months, the sun is too low (in the Netherlands) to produce vitamin D. You then use the stock you have built up.

However, there are many factors that can limit vitamin D production in the skin. Think of the use of sunscreen, time of day (the most favourable hours for vitamin D production are 11 a.m. – 3 p.m. but these hours are of course the most dangerous hours in terms of sunburn), skin tint, age (the older you are the less efficient your body is in producing vitamin D), clouds and smog.

Are vegans more at risk of a vitamin D deficiency than non-vegans?

In theory vegans are more at risk because they don’t get any vitamin D from food at all (unless they eat a lot of fortified foods). In the winter months, almost all of us produce too little vitamin D (I am talking about my country of residence, the Netherlands).

Vitamin D deficiency tends to be a population-wide problem, rather than a vegan-specific concern. It’s a nutrient of concern for both vegans and omnivores.

How much vitamin D do we need?

In the Netherlands, a recommended daily allowance (RDA) of 10 micrograms of vitamin D applies to everyone but persons over the age of 70. For them, the RDA is set to 20 micrograms per day.

Some groups need more vitamin D than they can get from sunlight and food. Children 0-4 years old, pregnant women, people with tinted or dark skin and persons in the age category of 50-69 years old are advised to supply 10 mcg vitamin D daily. As mentioned above, all persons > 70 years are recommended to take 20 mcg of vitamin D daily. Furthermore, supplementation advice applies throughout the year in the Netherlands regarding the category of “people who do not go outside much.”

In some other countries the RDA for vitamin D and supplementation advice is higher.

Which plant foods contain vitamin D?

In the Netherlands, vitamin D is added to margarine.

Vitamin D2 is formed in certain mushrooms and molds, but only when they are treated with ultraviolet. And even then, the amount of vitamin D is low in those foods, and it is poorly absorbed.

How do you recognize a vitamin D deficiency?

In fact, it is pretty much impossible to recognize a mild vitamin D deficiency.

People can develop vitamin D deficiency if the usual intake over time is below recommended levels, if exposure to sunlight is limited, if the liver or kidneys do not function properly (both organs are involved in the process of vitamin D break-down and absorption).

In children, vitamin D deficiency manifests as rickets, a disease caused by the bone tissue not mineralizing properly, which results in soft bones and skeletal abnormalities. In adults and adolescents, vitamin D deficiency can lead to osteomalacia, in which existing bone is mineralized incompletely or poorly during the remodeling process, leading to defective bones. Signs and symptoms of osteomalacia are similar to those of rickets and include bone deformities and pain, tetanic spasm (a spasm involving contractions which do not stop) and dental abnormalities. At this stage you are actually far too late.

A mild vitamin D deficiency is difficult to recognize. Many people with a vitamin D deficiency suffer from fatigue. But you can also get these kinds of complaints if you are deficient in other nutrients, for example iron, vitamin B12 or protein.

The easiest way to know if you are deficient in vitamin D is to ask your GP for a blood test.

What are the consequences of too much vitamin D?

An excessively high vitamin D intake can only occur as a result of using high dose supplements for a long term. This can cause calcium deposits in the body, which can lead to kidney damage and kidney stones.

How do you properly treat a vitamin D deficiency?

In the case of a confirmed vitamin D deficiency, supplementation is always the first aid (and not sun exposure). The dosage and duration of supplementation is determined by how bad the deficiency is. Your GP or dietitian can prescribe the best dose for you. I never recommend taking mega-doses of vitamin D. And never more than 100 mcg per day (4000 International Units), which is the officially acceptable upper limit.

Can you just take any vitamin D supplement, or do you have to pay attention to certain factors when selecting a supplement?

Both vitamin D2 and vitamin D3 are used in supplements. Both forms are active and do their job in our body. Vitamin D3 has a slightly stronger effect than vitamin D2. But! Vitamin D3 is mostly obtained from animal sources. So basically, if you want to make sure that vitamin D is vegan, you have to check the label.