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Can an excess of Vitamin D be harmful to your health?
Take vitamins and think they are all healthy for you? Think again – many are dangerously overused. Find out which ones may actually do you more harm than good.
By almost any measure, the use of vitamin D and other supplements among Americans is staggeringly high. More than half of all US adults report taking a vitamin or mineral supplement in the last month, according to data from the National Health and Nutrition Examination Survey (NHANES), at a cost of more than $14 billion a year.
What is less known — and certainly much less promoted — is that vitamin supplements are not without risks. In fact, nearly 60,000 cases of vitamin toxicity are reported each year to US poison control centers.
“There is a lot of promotion of vitamin mineral supplements,” said Katherine Tucker, PhD, a professor of nutritional epidemiology and director of the Center for Population Health at the University of Massachusetts-Lowell. “People hear about a study, on the Internet or TV, and tend to think, ‘If some is good, more is better.’ There is a lot of overuse and misuse.”
This misuse and overuse of vitamin supplements is driven by a number of unfounded assumptions.
“The most obvious one is that vitamin supplements are needed,” said Marion Nestle, PhD, MPH, an emeritus professor of nutrition, food studies, and public health at New York University, and the author of the book Food Politics. “I’m not aware of any convincing evidence that they make healthy people healthier.”
Other assumptions are that vitamin supplements are safer or more important for health than prescribed medications, and that patients can direct their own supplement use without physician guidance.
“Patients often have a hard time taking their meds, but they are taking these compounds,” said Eliseo Guallar, MD, MPH, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, where he studies the effects of nutrition on heart health. “There are people who are taking several supplements at the same time, taking high doses, or taking ones that are not that well tested. And that can have consequences.”
Some of these consequences include higher rates of cancer, heart failure, and even an increased risk of dying. Here are five vitamin supplements that experts say you should avoid.
1. Vitamin A
“Vitamin A is one of the best examples of [acute vitamin toxicity],” said Dr Guallar. Unlike water-soluble vitamins, in which excess is excreted in the urine, fat-soluble vitamins like A are stored in the body for longer periods of time. While those who take vitamin A may be concerned that they’re not getting enough of this nutrient, in fact the opposite is more often true: generally speaking, the body absorbs vitamin A very efficiently; however your body has no way of getting rid of vitamin A. If you take more than your body needs, it sits and builds up, leading to potentially severe health problems.
“For older people especially, you really should not take vitamin A and vitamin D,” said Dr Tucker. “Rather than having trouble absorbing vitamin A, they have trouble eliminating vitamin A, so it can become toxic and accumulate in your liver.”
2. Vitamin E
Besides solubility, another key indicator of vitamin overuse, and potential toxicity, is the difference between a vitamin’s recommended dietary allowance (RDA) and the amount delivered in a supplement found on the pharmacy shelf.
“With vitamin E, the amount that people get in the most common supplement is approximately 20 times what you get with diet,” said Dr Guallar. “Whenever people start taking supplements at those concentrations we have to be careful.”
In the short term, high levels of vitamin E can affect blood clotting and platelet formation. Over the long term, high levels of vitamin E have been linked to prostate cancer and higher rates of overall mortality.
3. Folic acid or Vitamin B9
Also known as folate, it is critical if you are planning to get pregnant to prevent neural tube defects in the baby. However, nutritionists are becoming concerned that the general population is now taking too much folate, with potentially serious adverse effects on the nervous system.
The RDA for folic acid in adults is 400 μg, however the safe upper limit as established by the National Academy of Medicine is only 2-1/2 times this amount, at 1000 μg. “If you take folic acid in the stable form that’s in vitamin supplements above 1000 μg, we are actually seeing some negative effects that are kind of scary,” said Dr Tucker.
And it’s easy to overdo folic acid and vitamin D, according to Dr Tucker, because many common foods, like breakfast cereals and refined grains, are already enriched with folic acid.
Studies have long established that too much folate can mask a vitamin B12 deficiency, but what researchers are now finding is that a high folic acid/low vitamin B12 environment can also lead to nerve damage. “It’s slow and progressive but it can become permanent,” said Dr Tucker. “It starts with tingling in your fingers or balance problems, and it can damage nerves in your hearing, eyes and even bladder function…We’re really worried about too much folic acid and we’re seeing it. About 2-4% of older people have too much.”
4. Vitamin D
Among supplements, vitamin D is currently one of the most controversial. Using a common threshold established by the National Academy of Medicine (formerly the Institute of Medicine), more than one-third of US adults are vitamin D deficient. And vitamin D is critical for strong bones, especially for those who live in northern climates and get limited exposure to the sun. A deficiency in vitamin D is associated with decreased bone density (osteoporosis), an increased risk of falls, and possibly fractures.
But not everyone agrees on what constitutes deficiency. In a 2016 editorial published in the New England Journal of Medicine, a group of influential nutrition experts argued that widespread claims of vitamin D deficiency are due to a “misinterpretation and misapplication of the Institute of Medicine reference values for nutrients — misunderstandings that can adversely affect patient care.”
According to the authors, less than 6% of Americans ages 1 to 70 are deficient and only 13% are in danger of not getting enough.
And, like other supplements, more does not mean better with vitamin D. According to the National Institutes of Health, excessive levels of vitamin D can raise calcium levels in the blood, leading to vascular and tissue calcification and eventually damage to the heart, blood vessels, and kidneys. Studies have also demonstrated that long-term high levels of vitamin D are linked to a greater risk of cancer at some sites like the pancreas, and higher rates of death from any cause.
5. Vitamin B6
Even though most children, adolescents, and adults in the United States consume the recommended amounts of vitamin B6, 28%–36% of the general population still uses supplements containing vitamin B6, according to the National Institutes of Health. And B6 is another example where the dosage in a supplement pill vastly exceeds the recommended dietary allowance as established by the FDA: The most common dosage in vitamin B6 pills is 76 times the amount of B6 an adult should get each day, and it is not uncommon to find pills that deliver 200 or even 350 times the recommended dietary allowance.
Like folate, another B vitamin, chronic overuse of vitamin B6 can lead to nerve damage that includes ataxia, or a loss of control of bodily movements. Too much vitamin B6 can also cause a host of other problems, from skin lesions to gastrointestinal issues like nausea and heartburn.
Could an abundance of Vitamin D and other vitamins have adverse effects on your health?
The bottom line is that all of the nutrition and vitamin experts interviewed agreed on one essential point: for patients with an established nutritional deficiency vitamin supplements can be immensely beneficial, but healthy adults eating a balanced diet should skip the supplements.
“I don’t see why they should be taking any supplement,” said Dr Guallar.
When asked which supplements are most commonly misused or overused, Dr Nestle was even more direct. “All of them,” she said.
- For a complete list of recommended dietary allowances for common vitamins, visit the National Institute of Medicine.
- For more information on specific vitamins and vitamin D, visit the NIH’s Office of Dietary Supplements fact sheets.
