Vitamin D – part II
In our last visit, I was recounting the story of a young woman who was found to have low vitamin D levels. Vitamin D is an important nutrient that is now considered important by many prescribers, and you may find yourself being tested for your VitD level.
I’m skeptical by nature, particularly when it relates to changes in how drugs are considered over time. I remember back in the day when there was concern over too much vitamin D in foods. Our recent story of Vitamin D supplementation raised this issue again and spurred me on to look further into appropriate and optimal Vitamin D levels.
So what is an optimal Vitamin D level?
We’ll have to do some traveling to consider folks who need to supplement VitD and folks who are at risk of too much VitD.
Tromso, Norway is an unusual town far North above the Arctic Circle. Because the warm water of the Atlantic Ocean circulated up the coast, Tromso has surprisingly tolerable temperatures. I visited Tromso in 2008 just after the summer solstice during the time of the “midnight sun”, when it is daylight (more like dusk, actually) 24 hours a day. Even during this peak sun exposure, there is not much sun; the sun is low in the sky and you do not have to worry much about sunburning in Tromso.
Scandinavians have evolved light skin to maximize Vitamin D production in their location which receives limited sunlight. I looked for the natural VitD level in Scandinavians, and found that culturally vitamin D is pretty much always supplemented with dietary sources like fish and cod liver oil. Mean values for Vitamin D in Scandinavians are around 20-25 ng/mL. BTW, polar bears store large amounts of VitD in their livers, making them dangerous to consume because of VitD toxicity.
My good friend, Dr. Uchenna Nwosu, is from Igbo Ukwu, Nigeria, a village famous for its 9th century bronze artifacts and Dr. Nwosu’s Apex Medical Center. Nigeria is just North of the equator and gets LOTS of sunlight throughout the year. Nwosu speaks of Nigeria as a tropical paradise; it would be a tourist destination but for the political and social instability and poor infrastructure.
In equatorial Africa, people have evolved very dark skin to protect against too much Vitamin D. The sun is strong throughout the year; white skin Scandinavians will definitely sunburn in Nigeria in just a few minutes. I looked at the natural levels of VitD in those living near the equator with dark skin; Nigerian women had mean VitD levels of 24 and an upper level of around 40 ng/mL. Interestingly, although Africans have naturally higher levels of Vitamin D, children can still suffer from rickets if they do not have enough calcium in their diet.
Our visit to Tromso and Igbo Ukwu can help us interpret some of the dietary recommendations regarding VitD. It is interesting that North or South, sun deprived or drowning in sunlight, that people cluster around VitD levels of 25 ng/mL. This is close to the recommended blood levels in the US. Also, the natural limit of around 40 ng/mL in Africa suggests that the US upper recommended limit of 50ng/mL is probably appropriate.
Recently, a letter to the New England Journal of Medicine noted that individuals in the US should emphasize receiving – through diet or supplementation – an appropriate amount of Vitamin D instead of targeting a specific blood level.
The recommended dietary allowance of vitamin D in the US is 600 IU (International Units) daily for adults and 800 IU for those over 70 years of age. Make sure you take calcium as well (at least 1500-200mg daily) for bone health. Some health professionals recommend higher amounts of VitD (1000 to 5000 IUs daily) for those with lower measured levels of VitD, but this increases the risk of too much Vitamin D.
If you are wondering about whether you are taking the right amount of vitamin D, you are not alone. Talk to your prescriber or pharmacist for advice on VitD supplementation or to arrange to have your blood level of Vit D measured. Your community pharmacist is there to help. Take care of yourself this Christmas season and throughout the year.
NIH Office of Dietary Supplements
Vitamin D Factsheet
Hilger, J et al: A systematic review of vitamin D status in populations worldwide.
British Journal of Nutrition 111: 23-45 (2013)
Durazo-Arvizu, RA et al: 25-Hydroxyvitamin D levels in African American and Nigerian Women. American Journal of Human Biology 25: 560-562 (2013)
Manson, JE et al: Vitamin D Deficiency – Is there really a pandemic?
New England Journal of Medicine 375: 1817-1820 (2016).