The Dark Side of Supplementation: More Cancer and Heart Disease?

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A Multi-Vitamin Tub.Similar to fruit and vegetables, we tend to associate the word ‘vitamin’ with health.

Go to any health store, and you’ll see employees waiting to guide you through the latest vitamins and supplements.

Mainstream magazines and websites run features on the best and most reputable vitamin brands.

Similarly, constant advertisements educate us on the benefits of 1-a-day multi-vitamins for the health of our family.

However, there’s a significant problem. Although vitamins are essential nutrients, certain vitamin supplements are likely ‘useless’ – and that’s at best.

While some studies claim vitamins provides no clear benefit, others suggest supplementation may raise the risk of cancer and heart disease.

This article cuts through the advertising and takes a look at the darker side of vitamin supplementation.

What Are Vitamins?

Put simply; vitamins are nutrients which our body requires in specific doses.

First of all, they are necessary for the human body to work in its optimal state. Vitamins offer a range of benefits from boosting the immune system to scavenging free radicals (1, 2).

Vitamins come in two forms; water-soluble and fat-soluble.

Water-soluble Vitamins

Water Soluble Vitamins Including Vitamin C and the B Vitamins.

There are nine water-soluble vitamins in total;

  • Vitamin B1 (thiamin)
  • B2 (riboflavin)
  • B3 (niacin)
  • B5 (pantothenic acid)
  • B6 (pyridoxine)
  • B7 (biotin)
  • B9 (folic acid)
  • B12 (cyanocobalamin)
  • Vitamin C (ascorbic acid)

Each of these vitamins quickly dissolves in water, meaning that the body rapidly uptakes them.

Unlike fat-soluble vitamins, any unnecessary (excess) amount of water-soluble vitamins cannot be stored by the body. Instead, the kidneys excrete what they don’t need through urine (3).

There isn’t much reason to supplement vitamin C, as we can easily obtain sufficient amounts from leafy greens and various fruits.

However, deficiencies in B vitamins can be an issue for people eating only small amounts of animal foods – especially B12 (4, 5).

For this reason, many vegetarians and vegans take supplemental B vitamins.

Key Point: We can rapidly metabolize water-soluble vitamins. Our body removes excessive levels of these nutrients through urination. Meat, fruit, and vegetables are the primary sources of water-soluble vitamins.

Fat Soluble Vitamins Including Vitamins A, D, E, and K.Fat-soluble Vitamins

There are four fat-soluble vitamins;

  • Vitamin A
  • Vitamin D
  • Vitamin E
  • Vitamin K

We can store these fat-soluble vitamins for an extended period. As a result, in excessive doses, it easier to build up potentially harmful amounts in the body.

However, this certainly isn’t common and shouldn’t occur in otherwise healthy people consuming a reasonable diet.

A vitamin intake potentially leading to toxicity would usually be from megadoses. This being the case, supplementation presents the greatest risk for this.

Key Point: Our body stores fat-soluble vitamins for use in the longer term. Due to this, it is possible for a prolonged excessive intake to cause harm. Fat-soluble vitamins predominantly come from animal foods.

Is Vitamin Supplementation Necessary?

Chat with friends and family, and you’ll hear many people claim to take a daily multi-vitamin to “protect” health.

While this belief is common, it shouldn’t be necessary.

For example, those eating a diet of reasonable quality—including nutrient-dense foods like fish, meat, nuts, fruit, and veg—should be consuming adequate amounts of vitamins.

As a result, improving diet quality should be the priority for anyone concerned about nutrient deficiencies. Unfortunately, in today’s day and age, many people subsist on ultra-processed foods.

Processing strips these highly refined food products of their vitamins and minerals, which leaves them offering next to no beneficial nutrients (6).

A good example of this is the commercial processing of milk.

Whole milk is full of healthy fat-soluble vitamins, but creating low-fat “skim” milk removes a significant proportion of these (7, 8).

To make up for this nutritional shortfall, the producers fortify skim milk with synthetic vitamins.

Supplementing with vitamins to make up for a bad diet is a pretty similar process.

The problem?

There are split opinions on vitamin supplementation; while some believe the amount we get from real food is enough, others disagree.

However, research suggests some synthetic vitamins do not have the same effect as those which occur naturally in real food (9, 10).

Therefore, is it sensible to take a synthetic version of every vitamin—every day—with a multivitamin pill?

For me, the answer to that question is no.

Key Point: Rather than taking daily pills to make up for a bad diet, improving dietary choices should be the priority.

Nature's Way 'Alive!' Once-Daily Multi-Vitamin Tub.The Dangers of Supplements

Are vitamin supplements beneficial…or potentially dangerous?

There is no generic answer to this, and it likely depends on the specific vitamin and dose, the individual’s situation, the overall diet, and many other possible factors.

This question is not black and white – and vitamins can be beneficial in certain circumstances.

Generally speaking though, we only ever hear the positives of supplementation, so let’s examine some potential dangers.

First of all, several high-quality studies—including systematic reviews and randomized controlled studies—have found concerning results in recent years;

  • A meta-analysis of 19 randomized controlled trials featuring 135,967 participants suggested vitamin E supplements can cause harm. The relationship between vitamin E dosage and all-cause mortality was “statistically significant” and the authors concluded that “high dosage vitamin E supplements may increase all-cause mortality and should be avoided” (11).
  • In the second Physician’s Health Study, a daily multivitamin did not affect major cardiovascular events or mortality in 14,461 participants (12).
  • A recent 2017 systematic review of 21 prior randomized studies also found vitamin supplements to be wholly ineffective in cancer patients. While the study didn’t find any serious adverse reactions, the researchers concluded that “no positive recommendation can be expressed” (13).

Overall, the biggest concerns over vitamins mostly relate to supplementation with vitamins A, E, and B vitamins.

Key Point: Large-scale systematic reviews show no benefit to vitamin supplementation. In fact, taking a multivitamin every day may even be harmful.

Links Between Supplements and Cancer

With fat-soluble vitamins, it’s certainly possible to consume too much (e.g. beef liver), and excessive doses can be a problem with supplements.

Regarding vitamin A, high-dose supplementation appears to increase the risk of various cancers – especially lung and gastric cancer (14, 15, 16, 17).

However, there are no such associations in the foods which are rich in the vitamin.

Additionally, a large-scale study conducted in 29,133 male smokers showed increased lung cancer rates (+16%) in those taking beta-carotene supplements (18).

Supplementation with vitamins B6 and B12 also appears to have links to lung cancer.

In fact, a very recent cohort study of 77,118 participants showed that male smokers with the highest levels of vitamin B6 had triple the risk of lung cancer compared to those who didn’t take supplements (19).

While correlation doesn’t equal causation, this data is statistically significant and concerning.

Key Point: Solid evidence suggests that synthetic B vitamins and vitamin A supplements may increase cancer risk.

Vitamin Supplementation and Cardiovascular Disease

Vitamin Capsules Arranged in the Shape of a Heart.For those of us who don’t get much sunlight, we should take large doses of vitamin D…right?

Well, not so fast…

First, people with higher circulating vitamin D levels have a lower risk of cardiovascular issues (20, 21, 22).

However, the primary source of vitamin D for the majority of people is sunshine.

If we specifically look at individuals supplementing with vitamin D, several studies have found potential concerns;

  • A review of the evidence shows that there’s a ‘dose-response curve’ on the relationship between vitamin D and vascular calcification (hardening of the arteries). Not only does vitamin D deficiency have links to this condition, but so does vitamin D excess. It’s important to remember that our body has a negative feedback loop which prevents ‘overdose’ on vitamin D from sunlight, but this does not exist with supplemental vitamin D (23).
  • Excess doses of vitamin D (what constitutes “excess” will vary depending on the individual) may lead to hypercalcemia. Hypercalcemia leads to the excessive formation of calcium deposits in our heart and other organs. Notably, sunlight cannot cause this condition, and it can only happen through supplementation. Another key point is that some studies place the ‘tolerable upper intake’ at 4,000 IU per day –  yet we can easily buy 10,000 IU tablets (24, 25).

All in all, supplementing with vitamin D may be helpful for those living in cold and dark places.

That said, regularly consuming excessive doses of vitamin D could have serious adverse effects.

Overall, sunlight and food-sources of vitamin D are preferable.

Vitamin E

Vitamin E is known for its powerful antioxidant abilities and for fighting inflammation (26, 27).

Therefore, the assumption that supplementing with the vitamin will decrease the risk of cardiovascular disease makes sense.

Unfortunately, yet again this isn’t the case – it appears to have no effect and—if anything—may increase the risk of cardiovascular events.

A range of studies show that;

  • Four years of vitamin E treatment did not affect cardiovascular outcomes in patients at high risk of cardiovascular events (28).
  • In a study examining the effects of omega-3 and vitamin E on heart attack survivors, omega-3 had a positive effect on lowering cardiovascular events. In contrast, Vitamin E had zero benefits (29).
  • A randomized, placebo-controlled trial of diabetic patients examined whether vitamin E supplementation reduces the risk of cancer and cardiovascular disease. However, there was no impact on cancer rates – and the patients using vitamin E suffered an increased rate of heart failure (30).
Key Point: Large randomized controlled studies indicate vitamin D (in excess) and vitamin E may contribute to cardiovascular problems.

Vitamin Supplementation and All-Cause Mortality

Picture of a Grim Reaper In Black Hood.

The data on vitamin supplements and mortality are varied and inconsistent.

Some studies show a slight positive effect and others indicate that vitamin supplements may mildly increase all-cause mortality.

A recent 2017 systematic review looking into this issue examined 49 primary prevention trials using vitamin supplements.

These studies involved a total number of 287,304 individuals, and the findings were that (31);

  • There was an overall 6% increase in the risk of mortality from ‘vitamin A’ supplements in the form of beta-carotene. Vitamin A supplements also increased the risk of cancer by 16% in this study.
  • Vitamin E may improve cardiovascular outcomes. However, it heightens the risk of all-cause mortality.
  • The effects of vitamin D on all-cause mortality risk were inconsistent. For instance, some studies showed negative outcomes while others saw a slight reduction in mortality risk. However, the researchers conclude that that “there is no convincing evidence that vitamin D supplements can reduce mortality risk among men and women“.
Key Point: According to studies, vitamins A and E appear to increase the risk of all-cause mortality.

The Antioxidant Paradox: Benefits of Free Radicals

You’ve probably heard of free radicals before.

If not, they are the opposite of antioxidants, and they can cause inflammatory damage to the body.

However, an interesting point often overlooked is that free radicals can also play a beneficial role.

In moderate amounts, they are involved in normal biological processes such as cellular signaling and immunity (32).

Like with many things, it’s likely that excessive amounts of free radicals are “bad” rather than just any amount at all.

The idea behind the ‘antioxidant paradox’ is that super-concentrated doses of antioxidants may deplete free-radicals too much.

As a result, we might not have enough to assist with the body’s normal biological functions.

Could this be the reason why some vitamin supplements appear to have a neutral—or possibly harmful—effect on our body?

Key Point: Just because something is beneficial for health doesn’t mean that massive amounts of it are good. This statement may be the case for antioxidants.

Final Thoughts

Firstly, certain vitamins can be very helpful in the right dose. Vitamin D3 is one such example for those who live in Northern areas far from the equator.

(Note: if you supplement with D3, ensuring sufficient intake of vitamin K2 is important)

Overall, it’s difficult to ascertain whether vitamin supplements have an overall positive or negative effect. However, a whole industry spends huge money marketing the benefits of vitamins, so it’s important to be aware of the potential drawbacks too.

In either case, the potential for harm isn’t the worst thing about products such as multivitamins. The most worrying thing is that many people take them every day thinking they are protecting themselves from ill health.

Given the lack of substantial evidence for this protection, these people may be wasting their money. Before commencing vitamin supplementation, it’s probably a good idea to consider whether you truly need them.

Most importantly, a healthy diet should always come first.

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tjMichael JosephVinceJerome KahnTim Recent comment authors
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Hello Michael,

I am taking solgar magnesium pills daily as i am on ketogenic diet and it contains 8.3 mg of b6. Should i switch to magnesium citrate or this amount of b6 is ok?

Thank you for your help,


I completely agree about supplementation. For most people, it won’t be necessary, especially for multivitamins and similar options. It also just seems foolish to supplement just for the off-chance it does some good.

After all, the industry is somewhat unregulated. Why put something into your body if there’s a decent chance you don’t need it anyway?

Jerome Kahn

You should know that bad pharma dose what I call tobacco science to promote illness. A couple of Vitamins, C & E are protective against cancer. The Linus Pauling and Ewan Cameron trial with about 10 grams a day of cancer had results better than any chemotherapy for colon cancer. Pharma then criticized the trial, and published their own to show otherwise. This is one way industry puts profits before people. I have a copy of the Journal article published by them. Antioxidants and aspirin in high dose significantly reduce cancer risk, as well as reducing the risk of metastasis.… Read more »


How am I supposed to take this seriously with zero references? If there are so many ‘recent scientific studies’ there should also be citations referenced for further study.