Unlike any other vitamin, vitamin D3 is actually a ‘pre-hormone’, which is converted by the body into (a) calcidiol, which helps the kidneys maintain healthy calcium levels, and (b) calcitriol, the body’s most powerful steroid hormone. Like other steroid hormones, calcitriol signals our genes to make the enzymes and proteins necessary for maintaining health. It also regulates cell growth. No wonder then that vitamin D3-deficiency is implicated in such a wide range of illnesses.

The best way to get vitamin D3 is to bare your skin and eyes to sunshine. In sunny climates, about 20 minutes’ direct exposure* to bright sunlight generates around 20,000 international units (iu - exposure through glass generates none). After 20,000iu have been produced, the same sunshine triggers the body to kill off any excess vitamin D3 in the skin!

Recent research concluded that the adult body actually only needs between 3,000 and 5,000iu a day, so its apparently excessive production given sufficient exposure to direct sunlight is currently a puzzle. However, zoologists know that Nature does not design systems as complex as the vitamin D steroid hormone system without good reason. 20,000iu production a day given half a chance is definitely the way evolution designed the human body.

View Vitamin Research Products' vitamin D3 1,000iu supplement

* People in northern climes like the UK may need half an hour.