Depends upon what latitude you live at. Where I am, the sun isn't strong enough to trigger synthesis from October until the end of April. After that you need

Depends upon what latitude you live at. Where I am, the sun isn't strong enough to trigger synthesis from October until the end of April. After that you need a lot of skin exposed to get anything, which is difficult 'cos it ain't that warm. There is a reason red hair appeared in Southern Scotland/Northern Ireland.