Where your D3 comes from

By the end of winter roughly one adult in five in Britain is low on vitamin D, and most of the rest of us are not far behind. The sun is too low from October to March for the skin to make it, we are indoors, and we have been told to fear the sun for the rest of the year.

So most people who take it, take D3, and D3 usually comes from one of three places. It can be synthesised in a lab. It can be extracted from lanolin, the grease in sheep's wool, which is where most of the D3 on the market comes from. Or it can be grown in lichen, the slow grey plant on rocks and old trees, which is one of the very few plant sources of D3 there is.

Ours is from a plant: pine.

Vitamin D contributes to the maintenance of normal bones, to normal muscle function and to the normal function of the immune system. We believe it does more than that: fewer of the bugs that go round the school, and a February that does not feel like a wall. It is also the reason K2 is in the scoop. D3 pulls calcium in, K2 puts it where it should go, and we would not put one in without the other.