Too much of a good thing: can you overdose on food supplements and vitamins?


More than $120 billion is spent on vitamins and various kinds of biologically active food supplements every year (2019 Global Supplement Report). According to the study “Trends in Dietary Supplement Use Among US Adults From 1999-2012”, in the USA alone more than half of adults take some form of weight loss or health improvement supplements. At the same time, the regulation of vitamins or dietary supplements is much less rigid than the regulation of drugs:  in the United States, the FDA is not authorized to check the safety and efficacy of supplements before they hit the consumer shelves.

Basically, manufacturers only need to ensure that their product is free of contaminants, labeled in full compliance with the regulations and that the composition is consistent with what is advertised. On the one hand, it seems quite logical: vitamins do not heal in the literal sense of the word, do not have an instant effect. On the other hand, many additives can interact with each other and even with drugs, affecting their effectiveness, enhancing or weakening the action. And in some cases, even cause significant harm to health and even life. Is it possible to get intoxicated with vitamins and are there maximum permissible doses? Let’s get the facts straight.

Fat vs Water

All vitamins can be divided into two groups: those that dissolve in water and those that are fat-soluble.

Water-soluble vitamins include vitamin C and B vitamins, they do not accumulate in body tissues, and are excreted in the urine. In most cases, water-soluble vitamins are not dangerous even if you significantly exceed the recommended dose. Yet, as with everything else, there are some exceptions. Thus, a constant and long-term intake of large doses of vitamin B6 can lead to serious damage to the nervous system, according to research “Niacin‐Induced Anicteric Microvesicular Steatotic Acute Liver Failure”. Another red flag described in “:Pyridoxine Toxicity Small Fiber Neuropathy With Dysautonomia: A Case Report” dwells on the excess of B3 vitamin which threatens to damage your liver.

Only four out of the thirteen known vitamins are water-soluble: vitamins A, E, D, and K. These vitamins do not dissolve in water and you do not pee them away. This means they are easily accumulated in the tissues of your body and therefore are potentially more toxic than water-soluble ones. Vitamin K is considered the least dangerous, for  the maximum permissible values for it ​​are not even established. It is critical to remember that regularly exceeding the permissible doses of other fat-soluble vitamins can trigger really dangerous consequences.

Side effects of overdosing

As mentioned above, most water-soluble vitamins do not pose a mortal danger to us, even in very large doses, but you should not exceed the recommended dosage. Here is a quick list of the unwelcome effects that you may experience taking too large doses of certain vitamins, both fat-soluble and those excreted with water.

Vitamin С

Too much of this vitamin can lead to gastrointestinal upset, while a single dose of more than 6 grams is likely to set your head on fire with migraine (Vitamin C (Ascorbic Acid).

Vitamin В3 (nicotinic acid)

If you take 1-3 grams of acid during the day, you may have an increase in blood pressure, blurred vision, abdominal pain, and serious liver damage.

Vitamin В6

Depending on the age, weight and health condition, taking this vitamin in a dose exceeding 1-6 grams per day, one can develop photophobia, nausea and heartburn, skin lesions, as well as serious damage may be done to the nervous system.

Vitamin В9 (folic acid)

Exceeding the recommended doses of this vitamin (which is almost always prescribed for pregnant women) can negatively affect your immune system, reduce cognitive abilities, and even mask vitamin B12 deficiency.

Vitamin А

Not only supplements but also foods rich in vitamin A can be dangerous. This vitamin accumulates in the tissues of the body and a systematic excess of the recommended daily dose is fraught with nausea and a serious increase in blood pressure.

In some cases, the excess may provoke a coma, while a single intake of 200 mg of a vitamin or a regular tenfold excess of the recommended dose can be lethal, as described in the study “Hypercalcaemia Secondary to Hypervitaminosis A in a Patient with Chronic Renal Failure”.

Vitamin D

If you consistently go too hard on this one, you risk experiencing appetite suppression, as well as a slow heartbeat and a dangerous increase in blood calcium levels (Vitamin D). What’s more, according to a study “Vitamin D Toxicity in Adults: A Case Series from an Area with Endemic Hypovitaminosis D”, a single intake of a megadose of the vitamin – 50,000 IU or more – can kill us at all, according to a study.

Vitamin Е

The abnormal saturation of vitamin E in the blood impairs its ability to coagulate, which ultimately can lead to the development of bleeding (including internal) and hemorrhagic stroke.


The scientifically approved calcium dosage is 1000 mg for people aged 19 to 50 and 1200 mg for those over 51. If these doses are significantly exceeded, dangerous plaques form inside blood vessels more actively, which can lead to serious diseases of the cardiovascular system, as was researched and backed by a research  “Calcium Intake From Diet and Supplements and the Risk of Coronary Artery Calcification and its Progression Among Older Adults: 10‐Year Follow‐up of the Multi‐Ethnic Study of Atherosclerosis“.

Why proper dosage matters

Even in countries with a high level of economic development, where people have access to a high-quality and varied diet, they still report a deficiency of certain vitamins. Synthetic vitamins and nutritional supplements are an easy and affordable way to support your health. However, it is also important to carefully follow all recommendations and in no case exceed the recommended dosage.

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