Vitamins: How much is too much?

Findings from Roy Morgan Research reveal that 8.7 million Australians (44.2% of the population aged 14+) take vitamins, minerals and supplements. The report says that people who watch what they eat (healthier eaters) are more likely to take supplements than those whose diets are lacking in fruit and vegetables.

There's a fair chance that you take supplements because of your interest in health but did you know that popping vitamins as a health bonus may put your health at risk?

With some vitamins, it is a case of a little is good but too much is downright dangerous.

You are at a greater risk if you pop more than one supplement and have processed foods or drinks that are health-boosted with added vitamins.

Excess of some vitamins is toxic and causes harm. Risk ranges from simple diarrhoea, stomach ache and fatigue to fragile bones, memory loss, and birth deformities.

Not all harm is immediately noticeable. Not all harm is reversible.

The damage and harm may be delayed and take several months or more of excessive use.

At high doses, vitamins begin to behave like medications. The correct dose of a prescription medication is important, too much is not better. The same is true for vitamins.

A simple case of too much of a good thing, but how much is too much?

Do you know whether you are safe or in a risky over-dose zone?

Risky supplements include vitamins A, B3, B6, C, folic acid, D, K and possibly E.

Vitamin choice is not easy. Supplements are not easy to compare. There is no standard rule for listing ingredients and doses. Price and packaging are no certain guide of quality or safety. Labels might declare some of the risks but take more than one preparation or double up on doses and you may be over-dosing without realising it.

There are thousands of different vitamin and mineral supplements. It would take more than a year for me to compare all supplements.

This article helps you find out whether you are getting too much of a good thing.

Vitamin K

It's a risky business to just head out and buy just any supplement if you take blood thinning (anti-coagulant) medications such as warfarin. A supplement with vitamin K could throw your blood clotting into dangerous chaos. The important aspect of warfarin-vitamin K balance is consistency. The hit and miss, occasional vitamin taker will have more chaotic blood tests than the person whose warfarin therapy has already been balanced against a daily vitamin dose. Before you suddenly stop or start a vitamin tablet that contains vitamin K, speak with your doctor.

For most people however, vitamin K is a low risk supplement. There is no toxic or safe threshold Upper Limit reported.

The Recommended Dietary Intake for vitamin K is 60 mcg for women, 70 mcg for men  (mcg is often written with a squiggly u with a long front tail, as ug) daily.

You need more, between 90 and 300 mcg, if you have had surgery that alters how the gastro-intestinal tract works (e.g. metabolic surgery or weight surgery, removal of part of stomach due to cancer). Check here for detail.

Why does surgery to the intestinal tract make a difference to how much vitamin K you need? Bacteria in the gastro-intestinal tract (GIT) manufacture the majority of a human's Vitamin K. Food sources of vitamin K account for a small amount.

It makes sense that a change to the colonies of bacteria that live in your intestinal tract upsets vitamin K production. Change maybe due to a course of antibiotics or an overgrowth with unhealthy bacteria due to acid imbalances, or surgery to the GIT. These alter the balance of bacteria. The resident bacteria may no longer produce enough vitamin K for your body.


Folate (folic acid), the vitamin so essential in pregnancy planning, is not without risk for everyone when taken in supplements. The immediate risk of too much is indirect and related to vitamin B12 deficiency. High doses of folic acid mask or exacerbate the more serious vitamin B12 deficiency symptoms of the nervous system (e.g. tingling and numbness in limbs, movement and coordination problems, visual disturbances, memory loss, disorientation and dementia). These serious problems are not always reversible.

Longer term, excess folic acid has bad effects on reproductive and developmental processes, and may increase cancer risk.

All in all not good and therefore not wise to take excessive folic acid.

Just 1000 mcg taken as folic acid in supplements is the Upper Limit. More than this is risky. Find all the Upper Limits in a table.

Vitamin B12 deficiency is not rare. You are at a higher risk if you are vegan, have had surgery to remove part of your intestinal tract, or are simply getting older and less able to absorb vitamin B12. Some medications to treat reflux (called H2 blockers or proton pump inhibitors) add to your woes.

The Recommended Dietary Intake for folate is 400 mcg daily for adults increasing to 600 mcg during pregnancy.

After metabolic surgery or weight surgery, the recommended intake is up to 800 mcg daily.

Vitamin D

Take too much vitamin D from supplements and you risk laying down calcium in all the wrong places such as the lining of your blood vessel walls. Too much may even cause fragile bones.

The Acceptable Recommended Intake for vitamin D is 5 mcg for men and women aged 19-50 yrs and 10 mcg for ages 51-70 yrs daily. The safe Upper Limit is 80 mcg (3200 IU) vitamin D.

It is surprisingly easy to exceed the safe upper limit when you take more than one vitamin preparation. Tally up all vitamins you take to get a grand total. A lack of caution or safety warning on labels doesn't make it safe to self-medicate with more than the suggested dose.

Know the conversions to be sure you tally up your dose shown on vitamin labels correctly. Cholecalciferol is another name for vitamin D on labels.

The conversion is: 1 IU vitamin D = 0.025 mcg cholecalciferol.
For example, 1000 IU vitamin D = 25 mcg cholecalciferol.

After metabolic surgery or weight surgery, the recommended intake changes to 75 mcg (3000 IU) daily.

If a blood test shows you are deficient in vitamin D, you will need a higher dose than the RDI until blood levels are restored. This dose may be temporarily above the Upper Limit.

Vitamin A

Vitamin A comes in two main forms in vitamin preparations: retinol and beta-carotene.

Retinol can be toxic but beta-carotene is not harmful. The safe Upper Limit for retinol is 3000 mcg (10000 IU) daily. Too much damages the liver. During pregnancy, excess vitamin A will cause irreversible birth defects and damage to baby. Excess vitamin A does permanent harm to unborn babies.

There is no Upper Limit for carotenes but you will probably notice when you've had more than enough because the palms of your hands, soles of your feet and even whites of your eyes may get a yellow-orange tinge.

The daily Recommended Dietary Intake for vitamin A is 700 mcg for women, 800 mcg during pregnancy, and 900 mcg for men.

After metabolic surgery or weight surgery, the recommended intake can be as high as 3000 mcg (10000 IU) daily depending on the type of surgery.

You will need to know a conversion factor to work out whether your supplement is giving you more than enough. Vitamin A is usually listed in either IU (International Units) or mcg (micrograms) retinol equivalents. Keep the measurement the same when you add different supplements together, either mcg or IU.

The conversion is: 1 IU retinol = 0.3 mcg retinol equivalents.
For example, 1000 IU retinol = 300 mcg and 3333 IU = 1000 mcg.

If a blood test shows you are deficient in vitamin A, you will be cautiously prescribed a higher dose than the RDI until blood levels are restored. This dose may be temporarily above the Upper Limit.

Vitamin E

Heralded as a vitamin to protect from heart and blood vessel disease, it would be easy to think that more is better. But no, there is an Upper Limit for vitamin E set at 300 mg alpha tocopherol equivalents (a common name for vitamin E on vitamin labels).

That's 30 times the daily Acceptable Recommended Intake of 10 mg for men, and more than 40 times the daily intake of 7 mg for women.

After metabolic surgery or weight surgery, the recommended intake increases to 15 mg daily, well below the safe upper limit.

Vitamin C

Although there is a lack of evidence to conclude excess vitamin C is toxic, a prudent Upper Limit of 1000 mg is set. Just two soluble fizzy vitamins a day hits this Upper Limit. Too much vitamin C gives some people the trots (diarrhoea and stomach ache).

For people with iron storage disease (haemochromatosis), too much vitamin C may increase iron absorption and so increase risk of damage to body tissue.

The Recommended Intake is a modest 45 mg daily for men and women, increasing to 60 mg daily during pregnancy.

The recommended intake doubles after selected metabolic surgeries: Gastric Sleeve, Roux en Y gastric Bypass (RYGB) and Biliopancreatic Diversion (BPD/DS). Check here for detail.

Vitamin B6 (pyridoxine)

It is a myth that excess B vitamins get flushed down the toilet. Sure your urine may change to a technicolour yellow-green but not all excess of B vitamins is disposed of before it does damage. B6 is one of the risky vitamins.

Too much over a long period of time is the problem. The symptoms of excess may include bone pain, lethargy, and muscle weakness, numbness and muscle twitch especially in the feet. The symptoms are usually reversible but it takes time. Allow 6 months for the symptoms to resolve.

The daily Recommended Intake is age and gender linked: 1.3 mg for women and men aged 31-50 yrs, 1.5 mg for women 51 yrs or more, and 1.7 mg for men aged 51 yrs or more.

The recommended intake doubles after selected metabolic surgeries (gastric sleeve, RYGB and BPD).

The daily and the daily Upper Limit is 50 mg as pyridoxine, which is more than 38 times the recommended daily intake.

Niacin (nicotinic acid, niacinamide)

Not to be confused with nicotine in cigarettes, niacin is a member of the B vitamin group. Take too much in the form of nicotinic acid and you may get flushing (hot blushing). High doses of nicotinic acid were once used to lower cholesterol levels but it didnÕt go down too well with users because of the all too common flushing side effect. For some, it may trigger a painful gout attack.

The daily Recommended Dietary Intake for adults is 14 mg for women, 16 mg for men, and 18 mg during pregnancy.

Double the Recommended Intake after selected metabolic surgeries (gastric sleeve, RYGB and BPD).

The form that niacin comes in vitamins makes a difference where the safe Upper Limit sits. As nicotinic acid, 35 mg is the Upper Limit. If taken in a supplement as nicotinamide, the Upper Limit is 900 mg. Be sure to know which of these your vitamin contains. Niacin supplements as nicotinamide are not recommended during pregnancy.

When might more than the Upper Limit be okay?

Your doctor or dietitian may recommend more than the Upper Limit to fix deficiencies. Never exceed the Upper Limit without supervision from a health professional who not only knows your health, medical and surgical situation but also checks blood test results. Do not adjust or cut back on prescribed vitamins without first checking with your health professional.

How to avoid a vitamin over-dose?

  1. Total up the risky vitamins across all your supplements. Check the unit of measure (g, mg, mcg, IU) is the same when you do the tally for each vitamin.
  2. Check the totals against the safe Upper Limits for each vitamin for your age (Table 1).
  3. Speak with the dietitian or doctor who prescribed the vitamins if your total exceeds the Upper Limit. You may be on a high dose to correct deficiency or avoid deficiencies linked to surgery, medication interactions or health conditions. Do not adjust the dose until you get their professional advice.
  4. Wean down to below the Upper Limits if you self-prescribed the vitamin supplements.
  5. Keep supplements locked away or on high shelves out of children's reach. Children are at a greater risk of vitamin overdose from supplements.



NHMRC. Nutrient Reference Values for Australia and New Zealand including Recommended Dietary Intakes Sept 2005
Parrott Julie et al. Review Article: American Society for Metabolic and Bariatric Surgery Integrated Health Nutritional Guidelines for the Surgical Weight Loss Patient 2016 Update: Micronutrients. Surgery for Obesity and Related Diseases 13 (2017) 727-741
Roy Morgan Research. Nature's Own: Australia's own favourite vitamin brand. Nov 2016 accessed online 30/7/17