I’m a Doctor and Warn You Never Take this Vitamin

Vitamins are essential for our health. Our bodies just cannot function without them. Although most of our vitamins are obtained from our diet, one-third of adults, and more than 50% of those over age 55, report taking daily vitamin supplements.  

People generally believe that vitamins must be safe, and that even if they don’t result in any benefit, they are unlikely to cause harm. It’s an unfortunate fact that this does not seem to be true. As a doctor, I am often asked:

  • Which vitamins are recommended? 
  • Is it safe to take vitamins?
  • Which vitamins might be dangerous?
  • What are the side effects of taking vitamins?
  • Are there any special points about taking vitamins safely?

Read on—and to ensure your health and the health of others, don’t miss these Signs Your Illness is Actually Coronavirus in Disguise.

I’m a Doctor and Warn You Never Take this Vitamin


The truth of the matter is that most people get all the vitamins they need from their diet. If your body has enough vitamins on board, if you take extra vitamins, you will simply excrete them in your urine and feces.

There is generally no need to take vitamin supplements. However, there are a few exceptions:

  • Folic acid – Pregnant women are advised to take 400 mcg folic acid per day. This is to help prevent the baby from developing neural tube defects (e.g. spina bifida).
  • Vitamin D  – The current recommendation is for UK adults, at least, is to take 10 mcg (400 IU) per day of vitamin D. This is because low levels of vitamin D are very common. This advice was issued in April at the start of the COVID-19 pandemic because vitamin D is made in the skin in sunlight, and people were only advised to go outside to exercise for 1 hour per day. As the winter is now approaching and the days are becoming shorter, it may be wise to top up vitamin D levels, because all respiratory infections are more common in the winter months, and vitamin D plays an important role in our immune defense.
medical or scientific researcher or doctor using looking at a clear solution in a laboratory

A 2016 review in the Advanced Pharmaceutical Bulletin reviewed all the good quality randomized controlled trials on the use of vitamins between 1993 -2015. The authors concluded that taking high doses of vitamins A, E, D, C, and folic acid did not always help prevent disease, and in some situations could be harmful. They proposed that vitamins should be only issued under the control of a trained pharmacist. Read on to learn which vitamins might be dangerous—and when?

Vitamine e pills


Vitamin E is a powerful antioxidant. Antioxidants are important molecules as they have many anti-cancer effects in the body. However, their effect is complex and too many can be harmful.

In many studies where vitamin E has been given to patients to try to reduce the incidence of cancer, cardiovascular disease, or death, there has been no significant benefit.

Some studies have looked at the effect of vitamin E to prevent prostate cancer, or lung cancer, have even found this led to a small increase in risk. 

It seems that there are risks associated with taking vitamin E at high doses.

Vitamin C pills spilling out of a jar

Vitamin C is also a potent antioxidant with many properties, highly beneficial for health. However, many large studies have failed to show that taking vitamin C supplements has any effect on reducing cardiovascular disease, cancer, or death.

Many people believe high dose vitamin C can prevent upper respiratory infections.  However, this does not appear to be the case. A 2013 Cochrane data review including 29 trials, and 11, 306 participants failed to show that taking vitamin C supplements prevented the common cold.

Vitamin C supplements may even be harmful. In one 2004 study, vitamin C supplements in diabetic women lead to an increase in the mortality from cardiovascular disease.

Adverse effects from vitamin C are only seen in those taking supplements. They are not seen when large amounts of vitamin C are ingested in food. 

taking vitamins

Vitamin A—also known as retinol—is largely derived from beta-carotene, the red/orange pigment in many vegetables such as carrots. Vitamin A is another powerful antioxidant. Studies have shown that by having a good dietary intake of vitamin A, the risk of cancer of the lung, breast, pancreas, and bladder, is reduced. However, taking vitamin A supplements does not seem to have the same effects.

For example, in the Beta Carotene and Retinol Efficacy Trial (CARET), 18,000 current or recent smokers, and asbestos workers, were randomly assigned to vitamin A or placebo and followed up. After 6 years there was a 28% increase in lung cancer and a 17% increase in mortality in the vitamin A group.

In pregnant women, high doses of vitamin A have been shown to increase the risk of neural tube defects by a factor of 3.5. Vitamin A is now regarded as teratogenic.

Although vitamin A is known to be important for bone growth, taking excess vitamin A is not necessarily beneficial. Vitamin A deficiency is associated with poor bone growth, but excess vitamin A results in increased bone resorption (bone clearance) with fragile bones and an increased risk of fracture.

This is a water-soluble B vitamin. Folate deficiency increases the risk of developing a new cancer, but excess folate also increases cancer risk, by increasing the rate of cancer cell growth.

In one 2009 Norwegian study, 6837 patients with cardiovascular disease were randomly assigned to either folic acid supplements or a placebo and followed up for 9 years. The folic acid group showed a significant increase in cancer outcomes and mortality compared to those on the placebos.

woman holding a vitamin pill

At one time, experts believed that vitamin D supplements could reduce the risk of colorectal cancer and bowel polyps. However, a large, 2006, randomized trial of 36,282 postmenopausal women who took calcium and vitamin D supplements for 7 years, did not show any reduction in colonic cancer incidence.

In the UK, calcium and vitamin D supplementation is recommended for perimenopausal or postmenopausal women at risk of osteoporosis, as it has been shown to improve bone mineral density and prevent fracture.

Woman feeling headache and touching her head.

Although most vitamins are well tolerated, side effects are possible with any types of medication. Always check with your healthcare provider if you have chronic medical conditions or take any other regular medication, before you start taking any new tablets, including vitamin supplements.

If you have any signs of an acute allergic reaction—acute anaphylaxis—after swallowing a vitamin tablet, you must seek urgent help immediately.

Vitamin E Side effects are rare. These include headaches, dizziness, abdominal cramps, diarrhea, tiredness, and skin rashes. Rarely, vitamin E can cause bleeding problems with nosebleeds, or bleeding gums.

Vitamin C Side effects are rare. These include headaches, flushing, nausea, vomiting, dizziness, and migraine at high doses. High doses of vitamin C may increase uric acid levels leading to kidney stones. Vitamin C may raise blood sugars in diabetic patients.

Vitamin A Side effects are rare. These include headache, fatigue, lethargy, abdominal pain, loss of appetite, and vomiting. Vitamin A can also cause skin drying and cracking, loss of skin (desquamation) and hair loss. At high doses, vitamin A can cause liver toxicity – you should not drink alcohol when taking any vitamin, A supplements.  This list is not exhaustive – always consult your doctor.

Folic acid Side effects are rare. These include – fatigue,  nausea, bloating, passing wind, malaise, and skin rashes. An increase in epileptic seizures has been reported. Some people complain of a bitter taste in the mouth. There may be an association with insomnia.

Vitamin D Side effects are rare. These include nausea, vomiting and skin rashes. Taking too much vitamin D may result in high levels of calcium – hypercalcemia – which is a serious medical condition, associated with confusion, muscle weakness and bone pain. Take your vitamin D supplements exactly as directed and do not be tempted to take too much.

Shot of woman nutritionist doctor writes the medical prescription for a correct diet on a desk with fruits, pills and supplements.

Beware of the fat-soluble vitamins, A, D, E, and K, which can potentially accumulate in the body and are more likely to cause toxicity. 

Although vitamins K1 and K2 are safe, synthetic vitamin K3 is known to be highly toxic.

Water-soluble vitamins, such as most of the B vitamins, are easily excreted from the body every day in the urine. These vitamins are not stored in the same way and are less likely to ever cause toxicity.

Man sitting at the table and taking vitamin D

The Recommended Dietary Allowance (RDA) – is the amount of vitamin you need every day to stay healthy.

  • The Tolerable Upper Intake Level (UL) is the maximum amount you should take before you are at risk of an overdose or serious side effects.

The UL is not stated on the product label. You can find out the RDA and UL online.

The RDA is much lower than the UL. If you stick to the RDA you should not run into problems.

Most nutritionists feel that taking a multivitamin is unnecessary if you are eating a healthy diet, but there may be a benefit to certain vitamins in certain situations. A good example is the current UK advice to take additional vitamin D during the current pandemic.

It’s important to note that some vitamins should be taken together, and some at sperate times.

For example, calcium and vitamin D are taken at the same time, but calcium prevents the absorption of iron from the gut, so calcium and iron should be taken at separate times.

professional physician talking to camera

We all need to think carefully about our health right now, in the midst of the COVID-19 pandemic. However, reaching for a bottle of vitamins will never be as good for you as eating a nutritious balanced diet. Your body is designed to absorb vitamins and minerals from food, not from supplements. These are less well absorbed and do not have the same effects as nutrients from natural food sources. If you are thinking about vitamins, why not concentrate of improving your diet instead? Far more delicious, safer, and much more interesting! And to further protect yourself, and to get through this pandemic without catching coronavirus, don’t miss these 35 Places You’re Most Likely to Catch COVID.

 Dr. Deborah Lee is a medical writer for Dr Fox Online Pharmacy.