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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Nutrients: Can You Have Too Much of a Good Thing?

February 27, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Healthy Lifestyle
Medical Myths
Nutrients: Can You Have Too Much of a Good Thing?
Nutrients: Can You Have Too Much of a Good Thing?
With all the pressure to do more for your health, it may be surprising to learn that there can be too much of a good thing, particularly "healthy" nutrients, whether in the diet or by taking supplements.
Harvard Medical School Commentary

Last reviewed February 27, 2013

You may feel like you’re getting advice from all sides: Increase your intake of calcium, iron, vegetables and water; exercise more; take more vitamins; use more sunscreen. Your doctors, your friends and family may reinforce the notion that you are not doing enough to improve your health or reduce risk of illness. In fact, when you also consider all the “routine” recommendations for medical care — a yearly physical examination; getting your eyes checked; seeing your dentist regularly; getting your vaccinations; getting tested for osteoporosis, heart disease, colon cancer, cervical cancer and so on — doing the “right things” may seem like a full-time job. And that’s if you’re perfectly healthy.

Too Much of a Good Thing

With all the pressure to do more for your health, it may be surprising to learn that in a number of situations, the problem is not too little but too much of a “good thing.” In a previous column, I discussed how having tests is not always helpful. In today's installment, the issue is how to avoid getting too much of a "healthy" nutrient, whether in the diet or by taking supplements.

Several rather common conditions are marked by too much of something that is usually good for us. These include:

    • Hemochromatosis — Due to a genetic mutation, the body absorbs too much iron from the diet and deposits it throughout the body. Although recommendations to take extra iron are common, particularly for women who lose blood each month during menstruation, iron overload is a condition in which taking extra iron is not a good idea.



  • Hypercalcemia — This condition is present when the blood level of calcium is high (hyper = high, calcemia = calcium in blood) for whatever reason. Among the more common causes are excessive intake of calcium and/or vitamin D, overactive parathyroid glands (called hyperparathyroidism, in which there is an excessive amount of parathyroid hormone, a hormone that regulates calcium levels in the blood), certain cancers, and sarcoidosis (a disease in which inflamed tissues convert too much vitamin D into its active form, leading to too much absorption of calcium from the intestinal tract). Again, because the diets of many women do not provide enough calcium, taking extra is a good idea as one way to prevent osteoporosis, but not for people with hypercalcemia or a tendency to develop it.



  • Hypervitaminosis A — If you take more than 50,000 IU a day (that is, more than 10 times the government’s recommended daily allowance, or RDA), you could wind up with problems related to too much vitamin A, including headache, nausea, vomiting, fatigue, irritability and dry skin. Elevated calcium develops due to bone breakdown, a process that also may lead to osteoporosis and bone fractures. Liver damage, hair loss, poor balance and visual problems may develop over time.



  • Vitamin D toxicity — If you take too much vitamin D or if you already have a condition, such as sarcoidosis, that makes you prone to having a high calcium level, you could develop hypercalcemia, as above.



  • Water overload — You can become quite ill if you have too much water in your system, whether due to drinking too much or due to a specific illness. Recommendations to drink more water abound, even for people who are healthy and have no obvious reason to be dehydrated; for them, extra water is almost surely unnecessary and occasionally harmful.

Even too much (or erratic) ingestion of certain fruits and vegetables can cause problems! If you eat broccoli in large quantities or in amounts that vary over time, its vitamin K content can counteract the blood thinning effects of a common blood thinner, warfarin (Coumadin). So, for people taking warfarin, broccoli and other foods that contain significant amount of vitamin K, such as spinach and Brussels sprouts, should probably be avoided or at least closely monitored with blood tests. And for grapefruit juice lovers, an interaction may increase the potency of certain medications such as cyclosporine, atorvastatin and diltiazem. If you take your medicines and the grapefruit juice at the same time each day, tell your doctors about your diet, and have proper monitoring regularly, you don’t necessarily have to give up grapefruit juice. (In fact, some people are able to reduce the dose of their medicine by regularly drinking grapefruit juice, but discuss this with your own doctor before pursuing it.)

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How Would You Know?

When there is “too much of a good thing” such as iron, calcium or water in the body, the initial symptoms may be subtle or nonspecific (meaning they could be due to many different things). In fact, there may be no symptoms at all. However, for most, routine testing usually identifies the problem. Common symptoms and findings related to the conditions mentioned above include:

  • Hypercalcemia or vitamin D toxicity — constipation, poor appetite, abdominal discomfort, kidney stones (usually with severe back pain), fatigue, poor mental function, anxiety, depression, weakness and elevated blood pressure
  • Hypervitaminosis A — dizziness, nausea and vomiting, blurred vision, sedation, lack of energy, hair loss, aches and pains all over, abnormal liver function (even leading to cirrhosis)
  • Water overload — nausea, lack of energy, headache, weight gain, poor concentration or mental function, seizures, breathing problems
  • Interaction between certain foods and blood thinners — easy bruising, blood in the stool, bleeding gums

For people with these symptoms, common blood tests, such as measures of blood counts, kidney and liver function, blood calcium and sodium levels will usually identify the problem. In addition, some physicians (though not all) screen routinely for many of these conditions. For example, some experts recommend screening every adult for hemochromatosis by measuring the amount of iron in the blood. There is no agreement, however, that this screening should be routine.

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What To Do?

With all the warnings about increasing one’s intake of a variety of nutrients, how can one avoid taking too much? For a start, read nutrition information labels, including the recommended daily allowance; do not increase the dose of supplements above what is recommended by your health care professional, and remember that “a little is good, more is better” is not always the best approach. See your health care professional if you have symptoms and ask for specific recommendations for vitamins and supplements with focus on your particular health problems or concerns — perhaps it would be best if you took no vitamins or supplements at all! Finally, keep an updated list of your medicines and supplements and let your doctor know exactly what you are taking.

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Recommendations for people to increase their intake of certain components of their diet or to add supplements may make sense for the “average person,” but it may not apply to you. It’s important to know when enough is enough and when to avoid certain nutrients or supplements that otherwise might be good for you. Know your medical conditions and whether there are specific recommendations not only about what to increase but also what to avoid. There can be too much of a good thing — and, depending on your condition, a “good thing” may not be good for you at all.

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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