by Vera H-C Chan Not in the mood? Blame your pasty complexion. A new study says hiding from the sun like a bridge troll may keep the libido at bay. Curious researchers from the Medical University of Graz , Austria, decided to follow some 2,299 men and measure their male sex hormone levels. They found a corresponding dip in vitamin D and testosterone in winter months starting in October. Men hit rock bottom right around Marchâ€"something to look forward to in the weeks ahead.