Vitamin Supplements

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Tablets taken by millions in UK every day could 'increase cancer risk by 30 per cent' 

Item half of British Adults take regularly linked to risk of early death

Daily multivitamins do not help people live longer, major study finds

Multivitamin Use and Mortality Risk in 3 Prospective US Cohorts
"In this cohort study of 390 124 US adults without a history of major chronic diseases, we did not find evidence to support improved longevity among healthy adults who regularly take multivitamins."

The Limited Value of Multivitamin Supplements (commenting on above):
"Considerable evidence now shows that, apart from the aforementioned roles for vitamin supplementation, there is little health rationale for the use of multivitamin supplements. Micronutrients come most healthfully from food sources. When supplementation is required, it can often be limited to the micronutrients in question."

Vitamin pills and risk of death

Nutritional Supplements and Cancer: Potential Benefits and Proven Harms

Vitamins, diet supplements and cancer
"There is no reliable evidence that dietary or nutritional supplements can prevent, cure or control the growth of cancer. Check with your specialist before you take any supplements to make sure they won't interfere with any cancer treatment you are having. " (CRUK)

Doctor warns commonly taken supplement could lead to "clots in the heart and brain"

Oncologist warns common pill could increase cancer risk 30 per cent 

"Omega-3 supplements could pose a significant risk, especially if taken daily without medical supervision."
"Taking omega-3 supplements on a chronic basis without medical advice has been associated with two major risks: the first, without any doubt, is atrial fibrillation."
"The second associated risk is increased bleeding." 

What are the risks of fish oil supplements? (From The Guardian)

Some studies have found that potent fish oil supplements can put people at higher risk of atrial fibrillation – an irregular heartbeat that can lead to blood clots, stroke and heart complications. One trial ["STRENGTH" trial] of 13,076 patients was halted in 2020 “based on evidence of a low chance of clinical benefit and a statistically significant increase in atrial fibrillation”:

From that trial, "STRENGTH Results prompt questions about Omega 3"

"Almost 20 million people in the U.S. take fish oil supplements, mostly because these products are advertised to reduce cardiovascular risk and claim unproven health benefits. ... The STRENGTH trial adds to the increasing evidence that fish oil supplementation, particularly when added to recommended statin therapy in high-risk patients, has no beneficial effect on cardiovascular risk."

Vitamin D

Pharmacist's vitamin D warning as some people are risking cancer
“Don’t take too much vitamin D. Because it’s a fat soluble vitamin it can build up in your body easier than other vitamins. Taking too much vitamin D long term can lead to hypercalcemia, an excess of calcium in the body, which can cause problems with your heart, kidneys and bones. 4,000 IU or 100 mcg is considered to be the upper limit of safe vitamin D supplementation.”

Vitamin C

Vitamin C: Scurvy Savior or Immune Overdose? More of a Good Thing Isn’t Always Better

Many sellers claim vitamin C supercharges immunity and is useful for preventing or treating diseases other than scurvy. Immunologist and microbiologist Andrea Love, PhD, looked at the issue in an effort to distinguish science from pseudoscience. Excess amounts of vitamin C can lead to serious gastrointestinal issues and “interfere with muscle recovery after exercise or other important immune-related processes,” she writes.

"While legitimate vitamin C deficiency can impact your health, there’s a big difference between that and claims that excess vitamin C is advantageous. Vitamin C deficiency is uncommon, especially in developed nations. Unfortunately, the wellness industry exploits people’s desire to take control over their health with clever marketing and vague science-adjacent statements. Even in the case of an essential nutrient such as vitamin C, if the claims sound too good to be true, that should be a sign that they are."

In this article, "The toxic effects of taking excess vitamin C" nutrition experts caution against its possible harmful effects:
Digestive - Acid reflux and heartburn, nausea and vomitting.
Kidney stones
Iron  overload threatening organ health.

Vitamin B6

This report shows the danger of excessive B6:

Simon never linked the pain in his hands and feet to multivitamins

"[He] has a nerve condition known as peripheral neuropathy as a result of consuming excessive vitamin B6, found in many multivitamins and magnesium supplements."

"A growing number of consumers are presenting with symptoms linked to high levels of vitamin B6, pathologists say, while the supplement industry goes unpoliced."

Vitamin A

From NHS advice:

Some research suggests that having more than an average of 1.5 mg (1,500 µg) a day of vitamin A over many years may affect your bones, making them more likely to fracture when you're older.

This is particularly important for older people, especially women, who are already at increased risk of osteoporosis, a condition that weakens bones.

If you eat liver or liver pâté more than once a week, you may be getting too much vitamin A.

Many multivitamins contain vitamin A. Other supplements, such as fish liver oil, are also high in vitamin A.

If you take supplements containing vitamin A, make sure your daily intake from food and supplements does not exceed 1.5 mg (1,500 µg).

If you eat liver every week, do not take supplements that contain vitamin A.

Calcium

This 2017 paper "Calcium supplementation and cardiovascular risk: A rising concern" concluded, "Along with previous data associating calcium supplementation with cardiovascular mortality and all‐cause mortality, this new evidence stresses the need for an evidence‐based approach to calcium supplementation. Moreover, it is urgent to educate health care providers on the possible risk of excessive and unnecessary calcium supplementation. From a cardiovascular perspective, dietary calcium intake by eating foods high in calcium appears safer than calcium loading with supplements."

[Author's comment: My father's death from myocardial infarction may have been from arterial calcification from excessive consumption calcium based antacids.]

Iron

From "The Dark Side of Iron" in Healthline, "Taking too much iron can cause toxicity and organ damage."

Dietary Supplements

Dietary Supplements – For Whom? The Current State of Knowledge about the Health Effects of Selected Supplement Use

Coming back to the original question in the title of the article, it should be stated that dietary supplements are not recommended for everyone to be used to generally support health and reduce the risk of diseases, but rather to be used by those people with a prolonged nutrient deficiency in their diet or a previously diagnosed deficiency in the body. Therefore, more emphasis should be given to dietary changes, including the benefits of eating more fruits and vegetables, where vitamins and minerals occur naturally in combination with other nutrients that cannot be replicated in food supplements. People who intend to take supplements on their own accord should not choose preparations with the highest nutrient content because, unlike ordinary foods, excessive intake may have serious health consequences. 

Supplements are necessary in cases of nutrient deficiency; however, even though prescription is not required, their use should be recommended and monitored by a physician. 

Published in Science Based Medicine October 2024:

Widespread Use of Dietary Supplements Linked to Liver Damage.

Millions of Americans are taking herbal remedies that may be toxic to the liver.

"Dietary supplements are enormously popular. With an economic impact of $159 billion (2023), it is somewhat (but not much) smaller than Big Pharma at $800 billion (2022). The category includes thousands of products, generally consumed with the aim of health improvement or maintenance. Some supplements have defined ingredients that have been well studied, where the risk of toxicity is understood. Other supplements may be sourced from plants (e.g., herbs) and by definition will be multi-ingredient – after all, herbal remedies with medicinal effects are effectively unrefined drugs. Toxicity risks with herbal remedies may be less clear, owing to their different and varying constituents. Because there is generally less regulation of supplements versus prescription or over-the-counter drugs, there may also be discrepancies between what’s on the label compared to what’s actually in the bottle, increasing the uncertainty about what you’re actually buying when you buy a herbal remedy."

Digestive Enzymes

What are Digestive Enzymes and do you need to take them?

Most people selling digestive enzymes, say that the symptoms of low digestive enzyme production are bloating, constipation, or diarrhea, or just general G.I. issues. While this is true, the problem with telling people this – besides the fact that most of us don’t have an enzyme deficiency and won’t benefit from these supplements –  is that these symptoms are vague and overlap with the symptoms from a lot of serious conditions. Influencers are not qualified to diagnose you with any of these.

Page last updated 8 April 2025