Shine On Me!
Why sunshine time alone doesn't guarantee that you have adequate Vitamin D levels.
By: Cameron Strouss and Dr. Thomas Slaughter III
Most people know that getting enough sun exposure is mandatory to regulate Vitamin D levels, but did you know that your skin makes Vitamin D precursors and those get absorbed and changed into active Vitamin D in the kidneys? A study in 1937 by Helmer and Jensen found that these precursors can be rinsed from the skin, and as such, are not available for reabsorption by the body.
“There is definitive evidence that the secretions from the skin contains precursors of vitamin D, which after irradiation are to be reabsorbed by the body, and the removal of which tends to produce a dearth of the vitamin unless it be supplied in some other form.” 
The most effective form to supplement with is Vitamin D3 (cholecalciferol). The most accepted RDA for D3 is 2000 i.u./day (micrograms) but I recommend 5,000 IU daily. For decades the FDA had the RDA @ 100 i.u. and strongly warned that to take more would be dangerous but it just isn’t true, so don’t be concerned. The dose of supplemental vitamin D3 and/or the amount of sunlight required to get people to the ideal blood range varies. Digestion, absorption, weight, skin color and genetics are all factors that have an influence on how much D you need. So, after 1 month of 5,000 IU daily, check your blood levels. Some people require up to 10,000 IU daily to get to adequate blood ranges. Optimal levels for a healthy person are 40-45ng/ml; however, some people with genetic factors and specific illnesses like autoimmune disorders need to raise their blood levels to 50-70ng/ml. Levels of Vitamin D over 70ng/ml increase your risk of kidney stones and show no concrete benefits.
Vitamin D is best taken with other fat soluble vitamins (A, K2, and E) because it helps the absorption rate. It is also extremely important to take your fat soluble vitamins with a healthy and fat-filled meal because it increases absorption and assimilation.
Low vitamin D levels has been associated with cancer prevention and with immune function, especially when dealing with auto-immune conditions such as Multiple Sclerosis, Hashimoto’s Thyroiditis, Rheumatoid Arthritis, etc. It is also instrumental in bone health, healthy childhood development, decreased instances and lowered severity of depression, and regulating blood pressure. Most Americans from beach bums to snow bunnies have been shown to be low in Vitamin D and I think we can contribute some of this to showering after outdoor activities, and not enough sun exposure to begin with.
So, get outside and stop showering so much! You can tell everyone your Herbalist said so, hehe. ;)
1. Helmer AC, Jensen CH: Vitamin D precursors removed from the skin by washing. Studies Inst Divi Thomae 1937, 1:207-216.