Dossier: Healthy eating

Vitamin D deficiency: what you need to know

Vitamin D, which the body produces itself in direct contact with sunlight, is essential for strong bones and a healthy immune system. Many people suffer from a vitamin D deficiency in the winter. Read on to find out who needs how much and whether we need to take supplements.

Text: Stefan Schweiger; photo: Sebastian Doerk

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What is vitamin D and why do we need it?

Strictly speaking, vitamin D isn’t actually a vitamin, because vitamins are supplied solely through food. Vitamin D is the overarching term for a group of fat-soluble vitamins called calciferols. In the body, it ensures that calcium and phosphate can be absorbed from the intestine and incorporated into the bones, making it essential for bone metabolism and other metabolic processes.

What is Vitamin D3?

When we talk about vitamin D, we really mean vitamin D3 – scientific name: cholecalciferol. Vitamin D3 supports bones metabolism, muscle function, brain function, the immune system, heart muscle cells and blood vessels.

How does the body produce vitamin D?

When the UVB rays in sunlight hit the skin, the body’s production of vitamin D runs at full speed. This is a complex process involving the skin, liver and kidneys. Once produced, this “sun hormone” is stored in the liver, in fatty tissue and in the muscles to be used later as and when needed.

As a rule of thumb for the lighter months: Half the time after which sunburn would be feared is sufficient – between five minutes and half an hour depending on your skin type, if possible without sun protection and without covering up. However, the sunlight has to be strong enough for this to work, and this isn’t the case in Switzerland from November to March.

What we eat only makes a minor contribution of between 10 and 20%.

“Vitamin D levels start to fall as early as November.”
Professor Heike A. Bischoff-Ferrari, professor for geriatrics and ageing research at UZH

Vitamin D deficiency: what to do

A low vitamin D level does not always have to be a cause for concern. It is quite normal for vitamin levels in the blood to fluctuate. Generally speaking, however: “The half-life of vitamin D in the blood is only three to six weeks,” explains doctor Heike Bischoff-Ferrari.

“In winter, vitamin D levels start to fall as early as November, which means that around 50% of people in Switzerland have too little vitamin D during the winter.” But how do you spot a vitamin D deficiency and how can vitamin D levels be increased?

What are the symptoms of vitamin D deficiency?

If you often feel tired and exhausted and often suffer from infections, this may be a sign that your body lacks vitamin D. Of course, these are pretty general symptoms. However, if you regularly have pain in the muscles or bones, these are clearer signs – in the worst case for a vitamin D deficiency that has been present for some time.

What causes vitamin D deficiency?

People with fair skin produce more vitamin D than people with dark skin, as a high melanin content in the latter reduces its production. People who cover their skin for religious reasons also have an increased risk of a deficiency. In addition, nicotine consumption lowers vitamin D levels.  

Risk groups: who is most often affected?

However, older people are more prone to vitamin D deficiency, because their skin produces up to four times less vitamin D. “This is made worse by the fact that older people tend to avoid direct exposure to the sun,” explains Bischoff-Ferrari. This even applies to senior citizens in Mediterranean countries as the temperatures are rising and becoming increasingly unpleasant. Windows and suncream block UVB rays,

which means that children also often have a deficiency. So should you take vitamin D supplements as a precaution? Yes, and the Federal Department of Health has recently increased its recommendation from 200 IU to 400 IU or 600 IU per day, depending on age.

What happens if the body lacks vitamin D?

A permanent lack of vitamin D affects the bones in particular. In the worst case, they can become soft – even leading to osteoporosis in older people. A vitamin D deficiency in infants and children can result in the bones not being supplied with sufficient nutrients, causing them to remain soft and warp – a disease known as rickets.

Do I have a vitamin D deficiency?

For adults, a level of vitamin D in the blood of 20 nanograms per millilitre (ng/ml) or above is generally considered adequate. Your family doctor can do a blood test to find out. Values of below 12 ng/mL coupled with typical symptoms such as bone or muscle pain indicate a vitamin D deficiency. Currents studies show that values over 30 ng/ml have no additional health benefits.

How is vitamin D deficiency treated?

The first measure should be to ensure you have enough exposure to sunlight, but without getting sunburn, of course. If that’s not enough, a vitamin supplement can be added to your diet – usually in the form of drops or tablets, available over the counter from pharmacies.

Bischoff-Ferrari says that you don’t necessarily have to have your vitamin D levels measured. “But it’s important to see your family doctor to learn about the risks and consequences of vitamin D deficiency.” It is also a good idea to have your risk of bone fractures and falls assessed. What’s more, recent studies show that vitamin D could protect against serious cancers and autoimmune diseases.

“We don’t recommend visiting a solarium to fill up on vitamin D.”
Professor Heike A. Bischoff-Ferrari, professor for geriatrics and ageing research at UZH

Preventing vitamin D deficiency

What’s the best way to prevent vitamin D deficiency: solarium, light therapy, diet or supplements? Four simple tips:

Go outdoors in winter, too

As there are fewer hours of sunlight in autumn and winter, it’s all the more important to make sure you get outdoors in the fresh air when you can and take advantage of them. The sun has to touch your skin, so go without sun protection for a short time!

Foods containing vitamin D

Admittedly, it isn’t always easy to get enough sunlight in winter. So, what foods can help? You can cover at least part of your vitamin D requirements by eating a lot of oily fish (salmon, herring or mackerel), mushrooms and eggs.

However, you can’t expect to cover more than 20% of your daily requirements. At 16 mcg per 100 g, salmon contains a comparatively high amount of vitamin D, while two eggs contain only 3 mcg. The German Society for Nutrition (DGE) recommends a daily intake of 20 mcg.

Do lamps or a solarium help against vitamin D deficiency?

Professor Bischoff-Ferrari advises against it: “We don’t recommend visiting a solarium to fill up on vitamin D, because they usually use a mix of UVB and UVA rays. UVA rays don’t boost vitamin D product and are harmful for the skin.” It increases the risk of skin ageing and tumours.

Should you take vitamin D supplements?

If you can’t get enough vitamin D from sunlight and diet alone, you can take vitamin D in the form of tablets or drops.

This is currently recommended for two risk groups in particular: children to prevent rickets (400 IU for children less than one year old, then 600 IU) and adults over the age of 65 (800 IU). IU is the international unit of measurement printed on the product packaging.

Incidentally, an overdose of sun rays only damages the skin, but taking too much vitamin D in tablet form can be harmful to health, leading to kidney damage in the long term, with symptoms such as nausea, stomach cramps and vomiting – a sign that calcium levels are too high – beforehand.

Video: How dangerous is vitamin D deficiency?

Prof. Dr. med. Heike Bischoff-Ferrari is Professor at the University of Zurich and leads Europe's largest healthy ageing study.

About the expert

Professor Heike Bischoff-Ferrari holds a chair at the University of Zurich and coordinates Europe’s largest interventional study on the topic of “Ageing healthily” (DO-HEALTH). She is also president of the Swiss Association Against Osteoporosis (SVGO) and president of the scientific advisory board of the Swiss public health programme “Connect” for recording and combating loneliness in Switzerland.

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