If you spend at least 15 minutes outside during the day and also eat a varied and healthy diet, you probably have enough vitamin D in your body. But what if you take extra vitamin D, in the form of supplements? For example, does that ‘do’ something for your training performance, muscle strength and muscle mass?

Key points:

1. Vitamin D is 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.

2. Adult men up to 70 years of age and women up to 50 years of age need 10 micrograms (400 IU) of vitamin D daily. The elderly need 20 micrograms per day.

3. As a young person, you normally meet this guideline if you go outside for at least 15 minutes in daylight every day, and eat a varied and healthy diet.

4. The elderly are advised to take a supplement to meet their higher vitamin D needs.

5. Also if you don’t go out much and/or if you follow a strict calorie-restricting diet (for example, bodybuilders in the cut), supplementation is recommended.

6. The elderly (50+) in particular may benefit from consuming more than the recommended 20 mg/day. Some studies indicate, for example, that high doses can help maintain and even build muscle mass, when combined with strength training.

7. Increased vitamin D levels may also have a positive effect on muscle strength in young people (aged under 50), but if so, the effect is probably very small or negligible. Moreover, there is no direct evidence whatsoever for a positive effect of vitamin D supplementation on muscle growth among young people. Among them, therefore, supplementation probably only makes sense if there is a vitamin D deficiency for a longer period of time.

8. Vitamin D supplementation can also increase the testosterone level, but that only has a noticeable positive effect in (older) men who have a vitamin D deficiency and (partly) as a result (too) low testosterone levels.

9. Although vitamin D is also important for the proper functioning of the immune system, it has not yet been scientifically proven that vitamin D supplementation makes more resistant to the coronavirus.

THE FUNCTION OF VITAMIN D

Vitamin D is a fat-soluble vitamin. This means that the presence of fat is necessary in the intestines to absorb vitamin D. This is in contrast to the water-soluble vitamins, which – you guessed it – do not dissolve in fat, but in water.

Vitamin D is necessary for the conversion of calcium from food. The vitamin 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 possible symptoms of a long-term (major) vitamin D deficiency are: muscle weakness, muscle tremors or cramps, joint and muscle pain, injury when pushed or bumped, and a higher risk of bone fractures.

VITAMIN D SOURCES

The main source of vitamin D is sunlight, to be precise: ultraviolet B radiation (UV-B). We make at least two thirds of the amount of vitamin D that we need per day, via synthesis.

We get the rest from the diet, provided there is a healthy and varied diet. Vitamin D is mainly found in fatty fish (such as salmon, herring and mackerel), and with somewhat lower levels in meat and eggs. As an indication: a salmon steak contains more than ten times more vitamin D than a piece of meat of a comparable size. Vitamin D is also added to low-fat margarine, margarine and baking and roasting products.

SUNLIGHT AND VITAMIN D

As mentioned, sunlight is the most important way to maintain the vitamin D level in your body. The Nutrition Center advises to be in the sun every day between 11 am and 3 pm with at least your head and hands uncovered in the sun. In cloudy weather it should be a little longer. Glass, such as car glass and window frames, blocks UV-B radiation, which is why you actually have to be outside in order to make vitamin D via sunlight ^[ i ] . Well, hanging out of an open window is of course also possible. Sunscreen also blocks UVB rays.

If you hardly go outside, you may not be producing enough vitamin D. You probably cannot fully compensate for a lack of vitamin D from sunlight by getting vitamin D from regular food. For people who are mainly indoors (in winter), a vitamin D deficiency is therefore quite real, especially if they also eat little or no fish. According to research, vitamin D deficiency is therefore common, even among relatively young people and more in urban areas than in rural areas ^[ xiii ] .

It goes without saying that in summer, if we are outside more often and for longer, we can produce more vitamin D than in winter. You do not have to worry that the vitamin D levels in your body will become too high, because your skin regulates the production. In practice, an overdose in healthy people rarely occurs, says the Nutrition Center. If it happens at all, it’s because of the use of supplements. The tolerable upper limit of vitamin D intake for adults and children 11 to 17 years of age is 100 micrograms (4000 IU) per day.

THE BENEFITS OF SUPPLEMENTS

As an adult man under the age of seventy and a woman under the age of fifty, you should take in about 10 micrograms (400 IU) of vitamin D per day, according to the Nutrition Center ^[ xiv ] . If you go outside every day during the day and you have a varied, healthy diet, that should not be a problem.

Insufficient exposure to sunlight, and in women over the age of fifty, men over the age of seventy, children up to three years of age, pregnant women, and people with dark or tan skin, do not produce enough vitamin D in the skin. skin. This lower production cannot be fully compensated with a healthy diet. Therefore, they must take extra vitamin D. This can be in the form of capsules, (chewable) tablets, oil or drops.

The best form of vitamin D is vitamin D3 (the “animal” form of vitamin D), which is also usually the form used in supplements.

Because of the relationship between vitamin D and the immune system, vitamin D may also be important to protect against the coronavirus. However , the scientific evidence for this is still thin ^[ ii ] .

VITAMIN D AND MUSCLE GROWTH/STRENGTH

For us strength athletes, the question is of course whether vitamin D supplements ‘do’ something for our main goal: muscle growth and/or strength increase.

Well, if a vitamin D deficiency is a real possibility for you, for example because you don’t go outside much and/or eat little fish and meat, supplementation is a must – also with a view to your muscle mass and strength. For example, a vitamin D deficiency can be accompanied by muscle weakness and muscle cramps. And that will undoubtedly not benefit your sports performance and muscle mass. Some experts even think that the usual decline in muscle strength in the elderly is not only due to old age, but also in part to a lack of vitamin D.

But what if you probably make enough vitamin D (10 or 20 mg per day, depending on your age)? As a strength athlete, can you benefit from even more vitamin D by using supplements? The short answer: maybe – a little. Especially if you are a bit older.

There are various studies into the effects of vitamin D supplementation on muscle mass and strength, the most important of which are listed below. Note that the subjects in these studies did not always necessarily have a (major) vitamin D deficiency. It is therefore not always clear whether the possible positive effects of supplementation also exist when vitamin D levels are already high enough without supplementation.

Agergaard et al (2005): vitamin D supplementation (48 mg/d) has a beneficial effect on muscle function in both young and old men, but no effect on muscle growth has been demonstrated (although too little vitamin D may have been supplemented for this). ^[ iii ] ;
Bunout ea (2011): Vitamin D supplementation (10 mg/d) helps to increase muscle strength in people over seventy who do strength training ^[ iv ] ;
Feldman et al (2011) (review): Vitamin D supplementation can help the elderly to counteract loss of muscle mass and strength ^[ v ] ;
Owens ea (2015): vitamin D3 supplementation (100 mg/d) helps men with a vitamin D deficiency to recover from muscle damage strength training and thus may have a positive effect on muscle growth ^[ vii ] ;
Chiang et al (2017) (review): Vitamin D3 supplementation (30 to 1000 mg/d) helps to increase muscle strength in trained individuals aged 18-45 ^[ vi ] ;
Han et al (2019) (meta-analysis): based on five studies, it can be stated that vitamin D3 supplementation has a small positive effect on strength performance, but mainly if your own vitamin D values are on the low side ^{[ xv ][ xvi ]} .

In short, especially among the elderly, vitamin D supplements could help (a little) to maintain muscle mass and strength, and improve their strength training performance (a little). These effects may be greater the higher doses are taken, even higher than the recommendations of the Nutrition Center (20 mg/day for men over seventy and women over fifty). Therefore, authorities abroad, such as the US and Canada, recommend higher doses, up to 50 mg/d. However, more research is needed to convincingly substantiate its usefulness.

VITAMIN D AND TESTOSTERONE

Vitamin D is also sometimes touted as a testosterone booster. In this way, the vitamin could also contribute, more indirectly, to muscle growth or maintenance. How about that?

Indeed, vitamin D also influences the production of testosterone, something that has emerged in a number of scientific studies. For example, men with a vitamin D deficiency appear to have significantly lower testosterone levels than men who have sufficient vitamin D in their blood ^[ viii ] . And older men with a low vitamin D level are less likely to have a (too) low testosterone level when they take vitamin D supplements ^{[ ix ] [ x ]} . Vitamin D supplements have also been shown to increase testosterone levels in overweight men (and therefore possibly low testosterone levels) ^[ xi ] .

Does that mean that vitamin D supplements are testosterone boosters? Not really. If your vitamin D status is normal and your testosterone level is within the normal range, vitamin D supplementation probably won’t have a noticeable effect on your testosterone levels ^[ xii ] .

IN SUMMARY

1. Vitamin D is 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.

2. Adult men up to 70 years of age and women up to 50 years of age need 10 micrograms (400 IU) of vitamin D daily. The elderly need 20 micrograms per day.

3. As a young person, you normally meet this guideline if you spend at least 15 minutes outside every day in daylight, and eat a varied and healthy diet.

4. It is best for the elderly to take a supplement to meet their higher vitamin D needs.

5. Also if you don’t go out much and/or if you follow a strict calorie-restricting diet (for example, bodybuilders in the cut), supplementation is recommended.

6. The elderly (50+) in particular may benefit from consuming more than the recommended 20 mg/day. For example, some studies indicate that high doses can contribute to maintaining and even building muscle mass, when combined with strength training.

Vitamin D How important for strength athletes?