What is vitamin D?
It is actually a fat-soluble hormone that is involved in calcium absorption and promotes bone mineralization. In addition to promoting bone health, new research suggests that Vitamin D may help prevent cancers, autoimmune diseases such as type I diabetes and cardiovascular disease.
How do we get adequate vitamin D?
When we are exposed to UV rays from the sun, Vitamin D is synthesized in the skin. In his book The Vitamin D Solution Dr. Michael Holick describes a way to calculate adequate sun exposure: first determine the amount of time in the sun to turn your skin pink then divide that time by 25-50%. It is then recommended that you get this amount of sun in March through May between 11am and 3pm 2-3 times per week. In June through August you can reduce the amount due to the higher levels of UV light in mid-summer. It is best to expose arms and legs to the sun and avoid the face. If you plan to be outside for longer periods apply sunscreen after the time it will take for adequate vitamin D synthesis.
Sun is definitely the best way to obtain vitamin D; however, older age, dark skin, obesity, some medications and living at more northern latitudes will lessen synthesis from the sun.
We may also obtain some vitamin D from fortified foods like milks and cereals, eggs, and some fish such as tuna and salmon, but these sources provide pretty insignificant amounts.
Is a vitamin D supplement good to take?
I very rarely see people who have what I would consider a normal vitamin D level (around 60ng/mL), so I typically recommend 1,000-2,000 IU daily taken with something fatty (like avacado or yogurt) since it is fat soluble. I recommend talking to your doctor about checking your vitamin D level before and after supplementation.
Is there a risk of getting too much vitamin D?
My sources show the body can synthesize 10,000-20,000 IU per hour with sunlight exposure in the summer with no harmful effects and no adverse effects have been seen with supplemental vitamin D intake up to 10,000 IU daily. Therefore, supplementation in the 2,000 IU range should be safe, but always consult with your doctor if you have any doubts or questions!
-Jenny Ward, MD