Vitamin D: Getting Your Right Dose

My grandfather had multiple sclerosis, which is an illness that is more prevalent in northern latitudes like South Dakota where he lived. Some researchers are investigating whether lower vitamin D levels might contribute to this trend. Data like this has increased our awareness of the need for vitamin D over the last few years. There seems to be an epidemic of vitamin D deficiency in this country especially since Americans are spending more time inside and doing a good job of using sun screen when outside. As I noted in a previous blog, exposure to toxic chemicals like pesticides might also be interfering with our ability to make vitamin D from sunlight. There is strong evidence showing that appropriate levels of vitamin D reduce falls and fractures and improve bone density. Vitamin D is also useful for helping prevent influenza and maybe even asthma attacks. Additionally, vitamin D might also help prevent some cancers and autoimmune diseases. Finally, I always make sure my patients that are taking calcium have adequate vitamin D levels. Without adequate vitamin D in the body, calcium supplements might increase heart disease, but when given together they reduced mortality by 9% in a recent study.

However, more isn’t always better. With all of the hype about vitamin D, I have seen people taking high doses for long periods of time. All medicines and supplements have optimal dose ranges: too little isn’t enough to help, but too much can cause problems. A common dose of vitamin D used to be 400 IU, but now the thinking is that this is probably too little. Likewise, regular dosing over 2000 IU might offer no additional benefit and in some cases may even diminish the desired outcome. For instance, in a study on influenza, Japanese children given vitamin D had a 64% reduction in the rate of influenza compared to placebo. But when children already taking vitamin D had more vitamin D added, their rate of the flu increased by 11%. This number wasn’t high enough to be sure it wasn’t just random fluctuations, but at the very least, it showed that more vitamin D didn’t lead to greater benefits. For Caucasian women with osteoporosis, higher doses didn’t necessarily have any negative consequences, but the increases in bone density were the same between two groups with one taking 800 IU and the other taking 6500 IU. While I sometimes recommend vitamin D testing, it is important to know that there are different optimal levels for different ethnicities. For instance, Caucasian women whose vitamin D levels less than 20 ng/ml had a significant increase in fracture risk, but African-American women whose levels were above 20 ng/ml had 45% increase in fracture risk. So while vitamin D can offer us several benefits, it is important to figure out your right dose.