The trouble is that supermarket multivitamins don’t contain the amount of Vit D required to make up for lack of sunlight in the UK; you need a high-strength D tablet in addition to the D in your multivitamin

(The UK govt recommends a 100IU supplement of Vit D per day and this is what most multivitamins provide, but current understanding is that an adult needs 1000-2000IU total per day, which is hard to achieve from sunlight and food in the UK)

Quite right. I recently started taking multivitamins, and was told by the doctor I need to take 800IU per-day (based on my blood levels) of Vitamin D (I have "Olive" skin), the multivitamin provides only half of that (400IU/10uG).

You shouldn't double up on the multivitamin or you'll be overdosing on other vitamins it contains, so an additional Vit D is required.

> The UK govt recommends a 100IU supplement [...] current understanding is that an adult needs 1000-2000IU

The NHS recommends you consider taking 400IU, and not more than 4,000IU: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-...

(That page also says 400IU is what adults need, do you have a source for your 'current understanding' by any chance?

> So I might as well take the multivitamin

It is possible to overdose on vitamins, and you can get adverse effects. It‘s not really a good idea to indiscriminately ”just take everything every day“.

Depends on the vitamin. It's difficult to overdose on Vitamin C for example. Vitamin D should be dosed with caution, but taking e. g. 1000 IU a day should be safe even if you get it from other sources.

That's true, but you have to do some really silly things to get to that point. You're not going to overdose on a multivitamin from the supermarket.

overdosing on Vitamin D is not really a thing

Hypercalcæmia?

Actually, it is possible to overdose on vitamin D, though it’s relatively rare. Vitamin D toxicity, also known as hypervitaminosis D, occurs when there is an excessive amount of vitamin D in the body. This can happen through very high doses of supplements over an extended period or by accidental ingestion of high-dose vitamin D supplements.

everything including water can be toxic at high doses. when I say its not really a thing, it means that it is indeed very uncommon compared to the amount of people who take supplements.

Ok, so paracetamol (aka Tylenol, acetaminophen) overdose is also 'not really a thing', because despite it being absolutely possible to trash your liver and die, the number of people who do that (including as a suicide attempt, as does happen) is miniscule compared to the approximately everybody who takes it.

The safety margin for Vitamin D is on a totally different scale vs the safety margin of Paracetamol (which is very thin, it's easy to overdose on it). bad analogies are bad.

Unfortunately, this is quite common among parents who want to make their own infant formula. They don't know how to dose milligrams and give ten or a hundred times the prescribed dose to infants.

https://www.anses.fr/en/content/vitamin-d-opt-medicines-avoi...

The blood test for vitamin D my doctor showed me includes a safe range.