He shared his tips on replenishing these reserves.
Get some sun – Depending on the time of day, month, and your location, there might not be enough UVB to produce vitamin D.
Most of us simply aren’t getting enough, especially here in the UK. Sensible sun exposure, particularly between 10am and 3pm, produces vitamin D in the skin that may last twice as long in your blood compared with vitamin D from supplements.
To make vitamin D, the sun must be high in the sky and this doesn’t happen in the UK between October and March. The shadow rule can help us work out whether the sun is in the right position to produce vitamin D.
source: express.co.uk