Nature medicine news has a short text about the sunshine cure.
The strongest evidence available is perhaps for the vitamin’s protective role in MS. Several studies have documented a dramatic ‘sunshine belt’ […] Latitude also seems to play a role in the incidence of hormone-dependent cancers. […] The effect is almost certainly because of vitamin D, Feldman says. “People tend to think it can’t do all these things when it’s a vitamin,” notes Feldman. “It’s not a vitamin, it’s a hormone.”