On a typical sunny day, your body may produce up to 25,000 international units (IU) of vitamin D, although many people aren’t in the sun enough to optimize their vitamin D levels. However, I strongly recommend getting your vitamin D from proper sun exposure, if possible, as it provides benefits beyond vitamin D optimization.
Higher levels of vitamin D may even serve as a marker for healthy sun exposure, which in turn may be responsible for many of the health benefits, which include reduced risk of cancer and increased longevity, attributed to vitamin D. Regular sun exposure, for instance, enhances the production of melatonin — a potent anticancer agent.
Near-infrared rays from the sun penetrate deep into your body and activate cytochrome c oxidase, which in turn stimulates the production of melatonin inside your mitochondria. Your mitochondria produce ATP, the energy currency of your body. A byproduct of this ATP production is reactive oxidative species (ROS), which are responsible for oxidative stress.
Excessive amounts of ROS will damage the mitochondria, contributing to suboptimal health, inflammation, and chronic health conditions such as diabetes, obesity, and thrombosis (blood clots). But melatonin essentially mops up ROS that damage your mitochondria. So, by getting plenty of sun exposure during the day, your mitochondria will be bathed in melatonin, thereby reducing oxidative stress.
If you’re unable to get adequate sun exposure each day, vitamin D supplementation may be necessary. Keep in mind that 20 ng/mL, which is often used as the cutoff for vitamin D deficiency, has repeatedly been shown to be grossly insufficient for good health and disease prevention, which means the true prevalence of people without optimal levels of vitamin D is even greater.
The only way to determine how much sun exposure is enough and/or how much vitamin D3 you need to take is to measure your vitamin D level, ideally twice a year. Once you’ve confirmed your vitamin D levels via testing, adjust your sun exposure and/or vitamin D3 supplementation accordingly. Then, remember to retest in three to four months to make sure you’ve reached your target level.
Resources: https://articles.mercola.com/