Vitamins
Is Vitamin D Toxic and Unnecessary?
Vitamin D deficiency is widespread, but fears about toxicity are unfounded. An overview of safety, proper dosing, and proven protection against respiratory infections.
Vitamins
Vitamin D deficiency is widespread, but fears about toxicity are unfounded. An overview of safety, proper dosing, and proven protection against respiratory infections.
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Vitamin D has been extensively and controversially discussed in recent years. It's promoted as a miracle cure just as often as it's warned against.
If you no longer know what or whom to believe, read on. But above all: stick with it, even if you can't hear the words "Vitamin D" anymore. ;-)
Vitamin D is undisputed an important substance in our bodies. More precisely, it's actually a hormone, because unlike vitamins, we can produce hormones ourselves. With vitamin D, this happens through absorption of UV-B radiation by the skin. In our latitudes, however, this can only occur from March to October. For the past two months, your body has been unable to synthesize vitamin D.
If someone now argues, "But we store vitamin D in fatty tissue," they'll be disappointed. This has all been calculated via scientific studies. Even well-stocked vitamin D stores—after plenty of sunbathing in summer—sustain us for at most one to two months. And only if we actively mobilize fats from fatty tissue ahem, ahem.
There's a good reason, then, that research paints a consistent picture: vitamin D deficiency is widespread across Central Europe, and Switzerland is no exception.¹ Studies such as Rabenberg et al. 2015 from neighbouring Germany found that the low threshold values for serum 25(OH)D levels of 50 nmol/l (= 20 ng/ml) are not reached on average—and up to 80–90% of the population is inadequately supplied in winter.² The situation in Switzerland is comparable. Wow!
So it's high time to supplement with vitamin D. Or is it? Not at all.
Everyone knows the headlines warning of the "serious consequences" of vitamin D supplementation. Yes, vitamin D can be harmful at way too high doses. As with everything, though. Remember: the dose makes the poison. Excessive vitamin D doses can lead to disruptions in calcium metabolism and unpleasant symptoms.
And yes: We also advocate gradually working up to the right vitamin D dose. You don't have to start with high doses right away. Meeting your needs in the range of 1,000–5,000 IU—and this can be very individual within this dosage range—is usually enough to benefit from vitamin D.
How safe vitamin D really is was demonstrated in the prestigious journal JAMA Network Open just last year.³ A meta-analysis of randomized controlled trials in children aged 0–6 years concluded:
"Vitamin D supplementation in the dosage ranges of 1,200 to 10,000 IU/day and single doses up to 600,000 IU can be well tolerated in young children."
Compared to the control group, there were simply no serious adverse effects—such as the infamous hypercalcemia—from high-dose vitamin D in children. For comparison: the standard recommended intake at this age is about 500 IU per day.
Studies in adults also showed that vitamin D supplementation over a period of more than 3 years leads neither to kidney stones nor to pathologically elevated calcium levels.⁴
Okay, okay, vitamin D is actually very safe. But what about infections? You read in the press over and over that vitamin D is unnecessary and doesn't protect against infections.
Let me recap: Vitamin D regulates over 1,000 genes—at least 5% of the entire human genome. Vitamin D regulates a variety of genes that affect immune function. Well documented for decades.
It seems to be a matter of belief again: believe the gloomy journalist without biology knowledge, or the world's best journal in endocrinology and metabolism? Let's listen.
A meta-analysis that evaluated 46 high-quality human studies involving 76,000 people on the topic of infection prevention through vitamin D, published in the prestigious journal The Lancet Diabetes & Endocrinology,⁵ identifies three key points under which vitamin D can truly prevent respiratory infections:
Then vitamin D reduces the risk of respiratory infections by 20–30%. For a single substance in the interplay of our lifestyle factors, that's quite a lot!
Vitamin D is safe and protects us. For us: avoid deficiency in winter. Even if we want to raise our vitamin D levels faster with somewhat higher doses, we run no risk of developing serious side effects.
We want to point out once more that vitamin D alone, of course, isn't enough to get us through the winter infection-free. This requires much more, for example: exercise, sauna/cold thermogenesis, plenty of high-quality protein, adequate selenium levels, more vitamin C, zinc, and more.
Let's get started!
(1) Robert Koch-Institut (2016). Vitamin-D-Status von Erwachsenen in Deutschland. doi:10.17886/RKI-GBE-2016-036.
(2) Rabenberg, M. et al. (2015) 'Vitamin D status among adults in Germany – results from the German health interview and Examination Survey for adults (DEGS1)', BMC Public Health, 15(1). doi:10.1186/s12889-015-2016-7.
(3) Brustad, N. et al. (2022) 'Safety of high-dose vitamin D supplementation among children aged 0 to 6 years', JAMA Network Open, 5(4). doi:10.1001/jamanetworkopen.2022.7410.
(4) Malihi, Z. et al. (2019) 'Monthly high-dose vitamin D supplementation does not increase kidney stone risk or serum calcium: Results from a randomized controlled trial', The American Journal of Clinical Nutrition, 109(6), pp. 1578–1587. doi:10.1093/ajcn/nqy378.
(5) Jolliffe, D.A. et al. (2021) 'Vitamin D supplementation to prevent acute respiratory infections: A systematic review and meta-analysis of aggregate data from randomised controlled trials', The Lancet Diabetes & Endocrinology, 9(5), pp. 276–292. doi:10.1016/s2213-8587(21)00051-6.
