1. Many people do not get enough sun exposure to create their own vitamin D. 2. Some bodies produce more Vitamin D for the same amount of sun exposure as other

1. Many people do not get enough sun exposure to create their own vitamin D. 2. Some bodies produce more Vitamin D for the same amount of sun exposure as other bodies. For example, darker skin produces less vitamin D. 3. Some bodies convert Vitamin D into other useful compounds less efficiently than others. This is commonly done in the liver and kidneys. 4. Those with Vitamin D deficiencies have problems with their muscles, bones, and immune systems. We do not fully understand the impact of Vitamin D, but it also seems to have an impact on mental health, and is a key part of SAD.