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"D" - The loser vitamin? Study results conflict - (9/18/2018)

By Dr. Ron Gasbarro 

If you get a D in algebra, you are lucky that you passed. If you take vitamin D, you are not doing much better, according to recent studies. For example, one large clinical study has revealed that taking a daily vitamin D supplement does not prevent bone fractures. Another new clinical study has found that extremely high doses of vitamin D do not prevent cancer. Haven’t we heard the opposite in other studies? Yes. Much of our confidence in the benefits of the sunshine vitamin came from studies of the supplements during the 1980s, which were never replicated and were flawed in terms of their study design. 

The largest clinical study ever performed on the benefits of vitamin D in preventing fractures was reported this year in the British Medical Journal. The study involved over 500,000 people. The results showed no significant association between vitamin D levels and the risk of fracture. But is this the truth? What is meant by a “significant association?” This means that some people actually benefitted from vitamin D for their condition. However, there were not enough of them to announce that D can prevent cracked bones or even cancer, your worst nightmare. What should we believe? After all, our bodies make vitamin D. Yet, we take supplements to avoid a vitamin D deficiency. The problem is that there is little agreement on what vitamin D deficiency is. Deficiency levels are arbitrary with no international consensus. A “normal” level can vary from 50 to 80 nanomoles (nmol) per liter of blood. Conversely, recent studies suggest 30 nmol is quite enough. Those who have vitamin D levels of 40 or 45 may be prescribed very high doses of vitamin D to get them back into the so-called normal zone. 

There are 2 things to know about vitamin D supplements. First, high doses of vitamin D can cause side effects. Because D is fat-soluble, it can hide in the cells and cause toxicities, such as extremely high blood levels of calcium (hypercalcemia). Symptoms of hypercalcemia include abdominal pain, bone pain, confusion, depression, weakness, kidney stones, or an abnormal heart rhythm including cardiac arrest. Second, we are all different and respond differently to chemicals such as medications and vitamins. Often our genetic background dictates how we respond to these chemicals. For instance, race has been reported to contribute to special dosing requirements for the blood thinner warfarin, with blacks requiring higher doses and Asians requiring lower doses than whites do. 

Patients with very high vitamin D blood levels (over 100 nmol) are becoming routine, and toxic overdoses are increasingly common. Several randomized trials have shown that patients with high blood levels or taking large daily doses of vitamin D (above 800 IU) had an unexpected increased risk of falls and fractures. Vitamin D was supposed to protect us from fractures. 

The bottom line is that we do not know how vitamin D supplements work. Yet, we need the vitamin so badly that nature has provided us with the means to make our own without the need for supplements. Vitamin D probably does prevent fracture and cancer in certain populations. We just do not know who benefits the most and at what doses. About half the US population takes vitamins daily, despite zero benefits, and with increasing evidence of harm. Instead of taking it as a dietary supplement, healthy people should get vitamin D from small doses of sunshine every day as well as from food, such as fish, meats, fruits, vegetables, and fortified dairy products. 

Ron Gasbarro, PharmD, is a registered pharmacist, medical writer, and principal at Rx-Press.com. Read more at www.rx-press.com


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