I doubt that's the case - for many years when I was a student I lived near equator and never went out. I never felt any impact or mind or body. I even tried some vitamin D3 supplement, smth like 2000IU but had no effects after few weeks, then I quit.

The biggest effect anything I had on me is Testosterone Enthante 250mg twice a week.

Also I wonder if taking 8,000 IU vitamin D can desentivize the system overtime