Updated: Apr 18
By Wageningen Beasts
A common scenario: summer has ended, autumn has come and it is not long before winter will start. The summer vibe is gone, motivation is down, energy levels are low and most of time is preferably spent in bed. There are multiple factors that could be causing this fatigue. It is often thought that vitamin D is the main contributing factor to this fatigue. However, there is still debate whether a shortage of vitamin D really causes fatigue. Nonetheless, a shortage can have some serious adverse health effects.
Vitamin D, also known as calciferol (and many other synonyms), has a remarkable feature compared to the other vitamins: it can be made (read: synthesized) by the body with the help of sunlight. However, with our current lifestyle of 9 to 5 desk jobs and modern technology we spend less time outside. Especially during the winter, when days are shorter and sunlight exposure is limited, we are prone to having a shortage of vitamin D.
What is a vitamin D shortage? Vitamin D has many functions in the body and is therefore an important mineral. Its main function is mineralization of the bones, but it is involved in many other functions (mineralization = a process of adding calcium and phosphor to the bones, making them dense). But what happens if you are vitamin D-deficient? A ‘real’ deficiency (such a big shortage of vitamin D that serious problems occur), that causes rickets in infants for example, does not occur that often and is quite rare. However, many people are vitamin-D insufficient, meaning they lack some vitamin D to function optimally. Vitamin D insufficiency can lead to a calcium deficiency, possibly an increased risk of several chronic diseases (such as some types of cancer and cardiovascular disease), a prevention of reaching the peak bone mass as an adolescent, and an accelerated loss of bone mass in adolescents which increases risk of osteoporosis. A calcium deficiency can also result in the above-mentioned problems. All in all, a vitamin D shortage should be avoided.
But how many people are actually vitamin D-deficient or insufficient? In clinical terms…
a vitamin D deficiency is a plasma 25-(OH)-D level (the level of active vitamin D in your blood plasma) below 30 nmol/L,
a vitamin D insufficiency is characterized by plasma levels between 30-50 nmol/L,
adequate levels of vitamin D are characterized by plasma levels above 50 nmol/L.
In Europe, 7-27% of the adult population has a plasma level below 30 nmol/L and are thus deficient, and 50% has levels under 50 nmol/L meaning that half of the population has insufficient vitamin D levels. You are more at risk of being deficient/insufficient if you are pregnant, have a dark skin or if you are above the age of 50. In conclusion, chances are high your levels during the winter are insufficient!
What are sources of vitamin D? As mentioned before, the body is able to synthesize vitamin D with the help of sunlight exposure. The human body makes an ‘inactive form’ (read: precursor) from cholesterol, which can then be activated by sunlight. If you spend enough time in the sun, you do not need any vitamin D from your diet to have a sufficient vitamin D level. But what if you do not spend enough time in the sun, which is often the case during the winter?
No need to worry, you can also get your intake of vitamin D through your diet, even if you don’t spend a minute in the sun. HOWEVER, getting a sufficient vitamin D intake from food only is not easy as not many foods contain vitamin D. Vitamin D is mainly present in egg yolks and fatty fish.
So how much vitamin D do you need? Recommendations for vitamin D intake are recently updated and increased, as research suggests that a higher intake can aid in obtaining optimal blood levels and numerous health benefits[1,2]. The table below shows the current recommendations of vitamin D intake (from either food or supplements). However, as mentioned before: getting your daily vitamin D from food is not easy. For illustration: 1 egg contains around 1,2 ug vitamin D. To get your daily D you need to eat around 10 eggs, which shows how hard it is to get sufficient vitamin D levels from nutrition (There is still debate about the health effects of eating so many eggs, and therefore having such a high consumption is not recommended).
This table is quite self explanatory. It shows the recommendations for the dosage of supplementation for different situations. In the age category of 4 to 50 (women) or to 70 (men), supplementation during the summer is not necessary. In all the other groups (during the winter or when you have dark skin/are pregnant/are a child/are an elderly or in menopause) you can benefit from vitamin D supplementation.
Vitamin D is still studied a lot in order to find the optimal intake, so it might be possible that recommendations will change more often.
How can you increase your vitamin D intake? There are a few options to increase your vitamin D levels during the winter. You can spend more time outside (especially when it is sunny) or you might eat more vitamin D-containing food products. A third, more efficient option is supplementation. During the winter, a vitamin D supplement of 10 ug per day might help in preventing a shortage, as diet is often insufficient in providing enough vitamin D. I would recommend a tablet of a cheap brand, as there is little difference between brands and these kind of supplements are often exploited by companies who want to make money (go to ‘De Tuinen’ and you know what I mean). Note: be careful with supplements and do not exceed dosages as indicated on the label, as high doses can lead to toxicity. Too much of anything is never good. Especially for vitamin D, as it is a fat-soluble vitamin, which means that the body cannot excrete excessive amounts.
Take home messages → During the Winter chances are high you are vitamin D-insufficient! → You can increase your vitamin D levels by eating foods such as egg yolks and fatty fish, spending more time outside or taking a vitamin D supplement with a dosage of 10 ug. → Be careful with vitamin D supplementation as high doses may lead to toxicity.
References  Whitney, E. N., & Rolfes, S. R. (2005). Understanding nutrition. Belmont, CA: Thomson/Wadsworth.  Peterlik, M., Boonen, S., Cross, H. S., & Lamberg-Allardt, C. (2009). Vitamin D and calcium insufficiency-related chronic diseases: an emerging world-wide public health problem. International journal of environmental research and public health, 6(10), 2585-2607.  Heaney, R. P. (2008). Vitamin D: criteria for safety and efficacy. Nutrition reviews, 66(suppl 2), S178-S181.  Health Council of the Netherlands. Evaluation of dietary reference values for vitamin D. The Hague: Health Council of the Netherlands, 2012; publication no. 2012/15E. ISBN 978-90-5549-933-5