> Another part of her point is that self-administering Vitamin D is far more dangerous than people, including many MDs, often think.

In absurdly high doses, sure. The Institute of Medicine certifies 4,000 IUs as the upper safe daily limit, although doctors will prescribe higher doses for people with a Vitamin D deficiency.

The Mayo clinic did a study of Vitamin D levels in 20,308 people across 10 years. The result was that 8% of people had Vitamin D levels higher than 50ng/ml (typically a sign of Vitamin D toxicity) but found no correlation between those levels of Vitamin D. They found one, one person out of 20k, who actually displayed symptoms of Vitamin D toxicity. Their blood levels of Vitamin D were over 350ng/ml. They had been taking 100k IUs (25x the suggested dose) as a routine daily supplement. I can only find one reported death from Vitamin D overdose, and it was a 10 year old boy who was mistakenly given 600,000 IUs of Vitamin D a day instead of growth hormone by a hospital in 2015.

Let's compare that to Tylenol (acetaminophen). Tylenol contains 500mg of acetaminophen. Maximum suggested daily dose is 8 tablets, so 4g. 25 times that is 100g. So someone abusing tylenol as hard as that person abused Vitamin D would be consuming 100g of tylenol a day. Medical literature suggests that you go to the ER immediately if you consume over 10g of acetaminophen. Of people who hit blood levels requiring treatment, 5% die and 58% have severe liver damage as a result. I can't find a good, easy correlation between the blood levels requiring treatment and amount taken, but I'm going to go out on a limb and guess that taking 200 Tylenols puts you there.

So if we compare the risk, relatively, Vitamin D requires you to take over 150 times your maximum daily dose for an extended period of time (dosing for children is lower than adults) to cause death. If you take 25x the amount of Tylenol once, there's a good chance you die or have severe long term outcomes.

Vitamin D is amazingly safe, provided you treat it like a medication and don't randomly swallow fist fulls of the capsules. Many people in the US (and some parts of Europe, especially in the north) should actually already be taking a supplement. Low Vitamin D levels are exceptionally common now. In the case of the US, obesity causes low Vitamin D levels, not going outside often enough causes low Vitamin D, and not eating foods containing vitamin D causes low Vitamin D. That's a disease practically tailored to our obese, couch-bound, junk-food inhaling residents. In northern Europe, I think they largely blame the seasonal changes in daylight patterns.

I'm all for calling out danger, I just don't see any here. I don't doubt that some people will manage to hurt themselves. I can already hear someone thinking "if 4,000 IUs keeps me a little safe, I can take 1,000,000 IUs and not wear a mask". If we're really that concerned that someone will harm themselves, we should be able to just add Vitamin D to the tracking system we use for Sudafed. Don't let anyone but more than 10k IUs per day. That's enough for 2 adults and a child at healthy doses, but low enough that taking that much every day is unlikely to harm you in the immediate future (and doesn't seem to be likely to harm you at all, but it is above the suggested dose).