When we think about vitamins, our main worries are usually focused on deficiency. We’re frequently warned about the dangers and symptoms associated with not getting enough of the nutrients we need to thrive and want to avoid getting sick. But what happens if you take too many vitamins?
It’s a scenario we rarely consider, but a very real possibility. If you’re taking a daily multivitamin along with high-strength boosters of certain supplements – a vitamin D spray, for example – and eating a nutritious balanced diet high in fortified foods, you might be overdoing it on the vitamin front without realising.
Unfortunately, taking too many vitamins and minerals can be as detrimental as ingesting barely any. And the effects can be so subtle, you might not even know you’re at risk. We asked Dr Deborah Lee of Dr Fox Online Pharmacy to explain the health effects associated with overdosing on vitamins:
What happens if you take too many vitamins?
Despite what you might’ve heard, it’s pretty much impossible to take too many vitamins from unfortified foods alone. For example, it’s been rumoured that eating multiple bananas is dangerous for your health since the fruit is high in potassium.
However, you would need to eat more than seven bananas to reach the recommended daily target of 3,500mg per day – and more than 42 bananas, ingested in a very short period of time, to become sick from a dietary overdose of the mineral.
‘On the whole, 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,’ says Dr Lee. However, a scientific review of quality randomised controlled trials surrounding the use of vitamins 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,’ she says.
Different types of vitamins
Not all vitamins are processed in the same way. Some are water-soluble, which means they are used rapidly your body, with any excess excreted through your urine rather than being stored in tissues. Because of this, they’re less dangerous even when consumed in large amounts. Water-soluble vitamins include:
- Vitamin C
- Vitamin B1 (thiamine)
- Vitamin B2 (riboflavin)
- Vitamin B3 (niacin)
- Vitamin B5 (pantothenic acid)
- Vitamin B6 (pyridoxine)
- Vitamin B7 (biotin)
- Vitamin B9 (folate)
- Vitamin B12 (cobalamin)
However, that’s not to say they’re safe to consume in unlimited amounts. For example, high levels of niacin (vitamin B3) can cause red skin flushes in some people, while too much vitamin B6 can lead to a loss of feeling in the arms and legs.
By contrast, fat-soluble vitamins do not dissolve in water and are easily stored in your body. Since your body stores these vitamins in your lives and fat tissues, it’s easier to accumulate in dangerous amounts, which could lead to hypervitaminosis (vitamin poisoning). The four fat-soluble vitamins are:
As well as the Recommended Dietary Allowance (RDA), which indicate how much of a specific nutrient your body needs on a daily basis, there is also a Tolerable Upper Intake Level (UL) that indicates the maximum dose of a nutrient that is unlikely to cause harm. Not all vitamins require these – for example, vitamin K has no observable toxicity even in high doses, so an upper limit has not been set.
However, that’s not to say vitamins that fall under this bracket are guaranteed to be totally safe in high doses. They may interact with certain medicines or have an undesired effect in people who have underlying health conditions. For this reason, it’s best to stick to the general recommendations unless advised otherwise by your healthcare practitioner.
Potential risks of taking too many vitamins
Like vitamin K, certain water-soluble vitamins appear to be relatively harmless at high doses and as such, have no set upper limit. These include vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B5 (pantothenic acid), vitamin B7 (biotin), and vitamin B12 (cobalamin).
However, the following vitamins have been ascribed upper limits due to their potential to cause harm at high doses, also known as megadoses. This can be through an acute toxic dose – a very high amount taken as a one-off – or a chronic toxic dose, which is a high amount taken consistently for an extended period of time:
Vitamin A toxicity occurs when you have too much vitamin A in your body. Symptoms may include nausea, vomiting, loss of appetite, abdominal pain, dizziness, irritability, drowsiness, headache, skin rash, increased intracranial pressure, coma and even death. The upper limit for adults is 3,000 mcg per day.
Vitamin B3 (niacin)
Common symptoms of vitamin B3 overdose include severe skin flushing, dizziness, irregular heartbeat, itching, nausea, vomiting, stomach pain, abdominal pain, gout, diarrhoea, loss of vision, high blood sugar and liver damage. The upper limit for adults is 35 mg per day.
Vitamin B6 (pyridoxine)
Symptoms of vitamin B6 toxicity include hyperaesthesia, paraesthesia, muscle weakness, numbness, loss of proprioception, skin lesions, sensitivity to light, nausea and heartburn. The upper limit for adults is 100 mg per day.
Vitamin B9 (folate)
Taking too much vitamin B9 may lead to abdominal cramps, sleep disorders, irritability, digestive issues, confusion, nausea, behaviour changes, skin reactions, seizures, and more. High intakes of folic acid may also mask a vitamin B12 deficiency. The upper limit for adults is 1,000 mcg per day.
Extremely high vitamin C intake can cause nausea, diarrhoea, and stomach cramps, and increase the risk of developing kidney stones. High amounts can be very dangerous for people with genetic conditions that cause an excessive build-up of iron in the body, and also people with diabetes. The upper limit for adults is 2,000 mg per day.
The main consequence of vitamin D toxicity is a buildup of calcium in your blood (hypercalcemia), which can cause nausea, vomiting, weakness, and potentially bone pain and kidney problems such as calcium stones. Other potential symptoms include weight loss, appetite loss, and irregular heartbeat. The upper limit for adults is 100 mcg per day.
Vitamin E is an anti-coagulant, so consuming excessive amounts may can cause blood thinning and lead to fatal bleeding or interfere with blood clotting. It and has also been linked to an increased risk of hemorrhagic stroke. The upper limit for adults is 1,100 mg per day.
Potential health risks aside, supplements containing high doses of water-soluble vitamins are likely to be a waste of money since you will end up flushing any excess down the toilet.
Can taking too many vitamins be lethal?
There have been reported instances of deaths related to vitamin toxicity, though they are extremely rare. This is usually where megadoses of certain vitamins have lead to serious complications, such as organ damage and failure. These lethal effects are associated with exceptionally high consumption.
For example, the recommended daily amount of vitamin A is 900 mcg for adult men and 700 mcg for adult women. Hypervitaminosis A can occur as a result of taking one large dose of vitamin A – 200 mg or more – or through chronic use of more than 10 times the recommended daily intake.
‘Although most vitamins are well tolerated, side effects are possible with any types of medication,’ says Dr Lee. ‘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 after swallowing a vitamin tablet, you must seek urgent help immediately.’
How to take vitamins safely
The best way for most of us to get enough vitamins is to eat a varied and balanced diet. However, certain groups are at at a higher risk of deficiencies than the general population, and they are recommended to use supplements. These include:
- Women who are trying to conceive or are in the first 12 weeks of pregnancy are recommended to take folic acid.
- The current recommendation is for all UK adults to take a vitamin D supplement.
- Children aged six months to five years should be given a supplement containing vitamins A, C and D.
- People who follow a vegan or vegetarian diet should take vitamin B12 and omega-3 fatty acids.
‘Some 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,’ says Dr Lee. ‘A good example is the current 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 separate times, she continues. ‘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.’
If you choose to take a vitamin supplement, pick one that contains no more than the daily recommended intake. If you are taking a multivitamin, there’s no need to worry about a vitamin overdose as they are designed for safe consumption even when combined with fortified foods. Vitamin supplements should never be used as a substitute for a balanced diet.
Last updated: 28-07-2020
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