Lightingman said
It’s a good idea to also take vitamin K2 with vitamin D, vitamin D aids calcium absorption and the K2 keeps calcium in the bones.
K is for the clotting cascade. It regulates itself, but as long as one has enough, more seems unlikely to help. Eat plants, and leave them in your colon for a while, and K should be sorted.
Athelstan Photography said
Natural vitamin D we get from the sun but very crucial for immune system and bones strengthen too. I take them tabs though quite regularly, Very effective.
D is essential for bones, and you can stand outside naked all day* in this season and you still won't make any, alas.
In Summer in England a quarter of an hour after coffee with your sleeves rolled up will give you your daily requirement and some spare. Probably twice as long if you've applied sunblock twice and spread it well not long before. I'm unconvinced it does much for the immune system, provided you are not rickety, and given the fiendish powers of auto-destruction the immune system - the adaptive one at least - demonstrates on some of us, I'd suggest that poking it to make it more active is not entirely wise. The old saying "let sleeping dogs lie" fails to cover it, try "let sleeping bears covered in porcupine quills and with the venomous thigh-spurs of a randy Platypus and a hangover lie".
Really, a touch of Vit D each winter day is almost certainly good for your bones and shouldn't give you kidney stones, and eating a fish finger each day as well won't be bad.
For many generations humans worried about eating, then for more they were interested in how much grit there was in what they ate, and now we are into the Hitchhikers Guide to the Galaxy phase of "where shall we have lunch?" It isn't the End of the Universe if you have a little extra of the definite vitamins, they are all very cheap, but retain scepticism.
* Occupationally relevant to some here perhaps