Viral infections occur in a predictable seasonal pattern increasing in prevalence during the colder months of the year. In fact, a low-grade viral infection is commonly referred to as a “cold” because of when it occurs.
What environmental factor varies with the seasons and affects our biology to such an extent that it influences our susceptibility to viral infection? The answer is sunshine, or more accurately, the predictable seasonal peaks and troughs of skin-produced, solar-generated vitamin D.
