Vitamin Supplements. Can you have too much of a good thing?

For as long as I can remember the idea of taking your vitamins on a daily basis has always been encouraged. Vitamins are nutrients the body needs to help regulate it’s functions and help maintain overall health. So it would make sense for some people to think that increasing your vitamin intake should keep in even better condition and health. This thinking is more prevalent now with people worrying about boosting their immune systems due to coronavirus fears. So many people should ask themselves, is there such a thing as taking too much vitamins and minerals?

Vitamin D

Although Vitamin D toxicities are rare they can occur. I’ve come across many a patient, especially elderly ones, buying high doses of Vitamin D (10,000 IU or 50,000 IU) thinking they should be taken daily. Many patients are wanting to “boost” their immune system by supplementing with Vitamin D. This can be tricky for healthy adults, in particular those already taking a multivitamin. Multivitamins have a dose of Vitamin D, which usually is enough to supplement unless their is an underlying deficiency or reason to increase the amount.

Healthy adults should be receiving 600 IU of Vitamin D with an upper intake limit of 4000 IU. A multivitamin usually has around 1000 IU so in addition with vitamin D already received in the diet, this should be enough for health adults with a balanced diet.

High intakes of Vitamin D for an extended period of time can lead to increase in urination (which can lead to dehydration), nausea, vomiting and weakness as a consequence of a buildup of calcium. One of the benefits of Vitamin D is it helps absorb Calcium to make strong bones but in this instance the calcium continues increasing. Vitamin D is stored in body fat so it is harder to “get rid of” compared to water soluble vitamins.

Verdict: Easy access to high Over-the-Counter doses. Although rare, complications arise with high doses over time.


There are many zinc containing used as a way to shorten the duration of colds as they help fight off bacteria and viruses. Now, with fears of coronavirus, people have been taking zinc as a preemptive measure. This can be dangerous for patients with low health literacy. They hear this is good for you and have no judgement when it comes to how much they should be taking unless they read the nutrition facts label (let’s be honest, few people do) or someone guides them as to how they should be taking zinc, if at all needed.

A healthy adult male should be getting around 11mg , a healthy adult female around 9mg and can go up to 12mg when pregnant. The highest intakes can reach up to 34mg of zinc for adult males and 40mg for adult females pregnant or otherwise. Always check what kind of zinc are you taking as the percent of elemental zinc varies between each form. It’s important to not exceed recommended upper limits of zinc supplementation unless under the care of a doctor during a treatment for certain conditions. Symptoms for acute zinc poisoning include nausea, vomiting, diarrhea, stomach cramps and headaches. Long term adverse effects include genitourinary complications, reduction in other micronutrients like copper producing anemia and reduced immune function, among other things.

Verdict: Small amounts are enough for overall health, with slight increases in dose for colds for a SHORT duration of time.


Magnesium is used by the body in many metabolic processes including nerve and muscle health. A prevalent trend is those who are exercising and weight lifting wanting to supplement with magnesium. For healthy adult males, depending on age, recommended magnesium intake ranges to around 410 to 420mg and for females 320 to 360mg. Multivitamins contain around 75mg which is not much but there are many magnesium containing foods which depending what meals you’re having, you might be getting a good dose in your diet. Depending on the demands of your body, in this case athletes, magnesium supplements can maintain muscle health if used appropriately.

Excess magnesium in our diet is excreted in the urine. Magnesium toxicity is rare and there is only a risk for those who are using very high doses of magnesium supplements (such as athletes) or magnesium-containing laxatives and antacids (such as infants, elderly people with chronic constipation). Those with kidney problems should exercise caution. Symptoms of magnesium toxicity include decrease in blood pressure, frequent urination leading to dehydration, flushing of the face, muscle weakness, nausea and vomiting.

Verdict: Specific people such as athletes can benefit. Those who take magnesium containing products in addition to multivitamins, such as infants and elderly people, should watch out.

Vitamin C

In the early days of COVID 19, Vitamin C was scarce. People left and right were trying to find Vitamin C supplements wanting to fortify their immune systems.

The good thing about Vitamin C is it has low toxicity and symptoms of abdominal cramps and other gastrointestinal effects are linked due to amounts of Vitamin C that haven’t been absorbed if you are supplementing with too much. There are other possible effects, such as impairing or increasing absorption of other nutrients in a harmful way, but they haven’t been proved 100%. Recommended intake should be 90mg for healthy men and 75mg for healthy women with upper limits reaching 2000mg. Some physicians recommend increasing intake during cold and flu’s in order to help the immune system fight off attack but others say this is just a placebo effect, meaning it’s all in your head- it doesn’t really work.

Verdict: Toxicity risk is low but benefits of high doses to immune system are constantly being called into question.


Office of Dietary Supplements – Zinc. Fact Sheet for Health Professionals. Accessed July 16, 2020

Disclaimer: all health-related posts are intended for educational purposes only. Consult your doctor before making any health-related decisions. Photos are for illustrative purposes only and does not constitute an affiliation with any entity.

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