Vitamin D is not a ‘true vitamin’, it’s actually a hormone. This is because once the ultraviolet B radiation from the sun penetrates our skin’s epidermis, our body begins the production of vitamin D, or specifically vitamin D3. Understanding this helps to explain why it’s inextricably tethered to so many biological functions.
There have been multiple studies that have correlated low vitamin D levels with increased infection and we now understand that vitamin D modulates both our innate and adaptive immune responses. This also ties into our understanding of the role seasons have in our fluctuating immune susceptibility. The cold weather we experience in winter doesn’t inherently cause a surge in influenza, but rather, the shorter days, decreased sunlight exposure leads to one thing – significantly less vitamin D – a biological breeding ground for illness susceptibility.
Deficiencies in vitamin D have been linked to increased vulnerability in muscle and bone related conditions, such as increasing one’s risk of osteopenia, precipitating and exacerbating osteoporosis, and increasing muscle weakness. This is because Vitamin D plays a synergistic role in supporting the absorption of calcium in to the body.