The benefits of vitamin D. Really though?
I've heard a lot from various sources and from my endocrinologist about the necessity of taking vitamin D, especially in northern latitudes. But after doing my own little research, I see this information.
Proven benefits:
- A 2023 meta-analysis showed a 6% reduction in overall mortality with long-term intake. The result only appeared when low-quality studies were excluded.
- A 2025 meta-analysis showed a 17% reduction in mortality in critically ill patients.
- Another study showed a 17% reduction in the risk of developing diabetes.
Proven harm:
- A Canadian study showed that doses of 10,000 IU per day reduced bone density by 3.5% over 3 years. Even 4,000 IU showed a negative trend. Yes, the vitamin for bones actually destroys them at high doses.
- Also, doses above 4,000 IU increase the risk of hypercalcemia and kidney stone formation.
What doesn't work:
- For people with levels >20 ng/ml there's no benefit for bones, for others there may be a small benefit (link).
- Zero effect for cardiovascular disease (link).
- No evidence of reduced cancer mortality (link).
- Minimal effect for respiratory infections (link).
At the same time, there's no consensus on vitamin D norms in blood — deficiency can be considered both below 20 ng/ml and 30. Moreover, studies show colossal individual differences in vitamin D requirements. And on top of that, optimal levels may differ for different ethnic groups. And it's worth noting the unreliability of testing — different laboratories can give different results for the same sample.
There are many studies, I haven't studied them all, but overall a picture emerges of some kind of casino from taking vitamin D — maybe red will come up (things will be slightly better), or maybe black (negative effects).
The vitamin D industry is worth billions of dollars, so it's quite logical to expect numerous recommendations for intake.
Irina Yakutenko has an interesting video about vitamins and dosages.