Vitamin D Level – Vitamin D is one of the few vitamins that’s hard to get enough of through diet alone. A limited number of foods contain vitamin D naturally – eggs, wild salmon, sardines, mushrooms exposed to UV light, and foods fortified with vitamin D. The best source is exposure to the sun. Your skin contains a compound called 7-dehydrocholesterol that’s activated by sunlight. When it’s “turned on”, it’s transformed into a vitamin D precursor. Once the vitamin D precursor forms, it’s processed by the liver and kidneys to make active vitamin D.
Do You Even Need Dietary Vitamin D?
Theoretically, you can get all of the vitamin D you need from the sun. UVA rays cause sunburn but it’s UVB rays that boost vitamin D production. However, you need direct sunlight. If you live in an area that gets little direct sunlight during much of the year, you’ll have to stay out in the sun longer to meet your vitamin D needs. Plus, many people wear sunscreens or simply don’t have the time to sit or stand outside with their skin exposed.
In addition, people with a dark skin pigment have to be out in the sun 5 to 10 times longer than a person with light skin to absorb the same amount of vitamin D. If you have light skin and live in an area that gets direct sunlight, 10 minutes of sun exposure daily will suffice. However, that’s not enough for folks with dark skin.
In addition, men and women over the age of 70 produce less vitamin from sun exposure than younger people. As a result, they need 3 to 4 times more sunlight to get the same amount of vitamin D as a younger person. Body weight matters too. Being obese reduces the bioavailability of vitamin D, so the body has a harder time accessing and using vitamin D. Because of these limitations, deficiency is common among people who are overweight and even in healthy, lean people. Some studies estimate that 75% of people are either deficient or borderline deficient.
To bolster flagging vitamin D levels, vitamin D supplements have become popular. No wonder! Most of us lead busy, fast-paced lives and have little time to sit outside with our skin exposed. Plus, pollution in the air is reducing the number of UVB rays that actually reach our skin to boost vitamin D. The current RDA for vitamin D is 600 I.U. of vitamin D daily and 800 I.U. for people over the age of 70. This is the quantity needed for healthy calcium metabolism and for bone health for the average person. However, this may not be enough to raise vitamin D levels optimally in everyone. That’s why you hear experts recommending 1,000 I.U. units or more daily and sometimes up to 5,000 I.U. Most studies show vitamin D doesn’t become toxic until daily doses of 10,000 I.U. are reached.
Still, more vitamin D, beyond a certain point, may not be better. Some studies show a u-shaped curve where low levels of vitamin D are associated with increased mortality, but high levels of vitamin D are too. One of the largest studies followed 250,000 people for seven years. It showed men and women with the lowest levels of vitamin D had a higher rate of mortality but so did those with the highest levels. The “sweet spot” seems to be between 30 and 50 ng/ml. Since some studies show cancer rates drop as vitamin D levels rise to 40 ng/ml and above, between 40 and 50 ng/ml is optimal, based on the information we have so far. However, there is some evidence that if you have certain autoimmune diseases, like multiple sclerosis, a higher level may be beneficial.
Optimizing Your Vitamin D Level
If you can get your vitamin D from exposing skin to sunlight and by eating vitamin D-rich foods regularly, that’s the best way. It’s impossible to develop a toxic level of vitamin D through sun exposure since sunlight-induced vitamin D production shuts down as vitamin D levels rise beyond a certain point. But for older people, those who are obese, and folks with dark skin, getting enough vitamin D from sunlight and diet alone is challenging. That’s where supplements come in. Vitamin D supplements can raise your vitamin D levels, although it takes time. If you’re already deficient in vitamin D. you may need a substantial dose for a short period of time to bring your levels up.
Should you just buy a vitamin D supplement and start taking it? It’s better to know your starting point. Although it’s safe for most people to take 1,000 to 2,000 I.U. daily, you’ll likely need to take more than this if you’re deficient. Instead, ask your physician to check a 25-hydroxy vitamin D level. Once you get the results back, you’ll have a better idea of how much you should be taking and whether you need a supplement at all. If you already have an optimal vitamin D level, you’re doing something right and may not need to make changes other than to monitor your level periodically.
If your vitamin D level is low, your physician can tell you how much to take daily to get your level into the optimal range. Once you start taking a supplement, recheck your level in 3 months and see how you’re coming along. You may need to adjust the dosage based on the results.
There’s another reason not to blindly grab a bottle of vitamin D supplements and take a high dose every day. Vitamin D is a regulator of calcium. There’s growing evidence that you need adequate amounts of vitamin K2 in your diet to balance out the effects of vitamin D and calcium. Vitamin K2 helps to transport calcium into the bones, where you want it, and keep out of the walls of your arteries where it could build up and cause atherosclerosis. A high blood level of vitamin D throws the balance between calcium, vitamin D, and vitamin K2 off.
The Bottom Line
The amount of vitamin D you need depends on what your vitamin D level is. Rather than guess how much you need, consider getting your level checked so you can adjust your intake to optimize your level.
American Cancer Society. “Vitamin D and Cancer Risk: Is There an U-Shaped Association?”
The Proceedings of the Nutrition Society 67, 146-156, doi:10.1017/S0029665108006988 (2008).
The Journal of Clinical Endocrinology and Metabolism, 2015 Jun;100(6):2339-46. doi: 10.1210/jc.2014-4551, Epub 2015 Feb 24.
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