Taking supplements to stay healthy is an attractive proposition.
Modern life can be busy, but taking medication is a convenient solution.
But rewards in life are rarely easy, and shortcuts can be dangerous.
Vitamin supplements are based on tenuous evidence at best and carry the risk of overdosing.
Here are six vitamin supplements that carry hidden health risks.
Vitamin A
Vitamin A is the fat-soluble vitamin known to be most effective in maintaining eye health.
Vitamin A comes in two forms: active vitamin A (a retinoid), which is commonly found in animal foods, and provitamin A (a carotenoid), which is found in colorful fruits and vegetables. Vitamin A is stored in the liver and helps prevent hypervitaminosis (abnormally high levels of a vitamin).
Research has shown that taking too much vitamin A can cause acute and chronic side effects, including headaches, muscle and joint pain, liver dysfunction, reduced bone health, and skin changes.
Acute vitamin A toxicity (called hypervitaminosis A) has been documented in Arctic explorers who ingested large amounts of animal liver and can cause rashes, abdominal pain, vomiting, and increased intracranial pressure, but these cases are extremely rare.
Additionally, vitamin A is known to be teratogenic and can cause fetal malformations, so women planning to become pregnant should avoid treatments containing retinoids, such as tretinoin.
How much is safe to take?
Some research suggests that consuming an average of more than 1.5 mg (1,500 µg) of vitamin A per day over many years may affect your bones, making them more susceptible to fractures in older age.
If you take supplements containing vitamin A, the NHS advises to make sure your daily intake from food and supplements does not exceed 1.5 mg (1,500 µg).
Vitamin D
Vitamin D is another fat-soluble vitamin that can put you in danger zone.
The “sunshine vitamin” is the primary vitamin that regulates calcium balance and is essential for healthy bone development.
During the winter months, many people turn to supplements to meet their vitamin D needs, but Taylor warns that this can lead to “chronic overdose”.
Symptoms include fatigue, nausea, diarrhea, and hypercalcemia (when calcium levels in the blood are too high).
Research shows this can lead to weakened bones, kidney stones, and impaired heart and brain function.
Other studies have shown that taking more than 10,000 IU (about 250 micrograms) of vitamin D per day can cause hypercalcemia, which can lead to kidney stones and abdominal pain.
The paper found that this, combined with abnormally high calcium intake, may increase the risk of developing colon polyps (tumours on the lining of the large intestine that can become cancerous) and having a stroke.
Research has shown that in extreme cases, vitamin D toxicity can lead to kidney failure, calcification of soft tissues throughout the body (including coronary blood vessels and heart valves), cardiac arrhythmias, and even death.
How much is safe to take?
If you take a vitamin D supplement, the NHS says that 10 micrograms a day is enough for most people.
Do not take more than 100 micrograms (4,000 IU) of vitamin D per day as this may be harmful.
This applies to adults, including pregnant and breastfeeding women, older adults, and children between 11 and 17 years of age.
Vitamin E
Vitamin E helps maintain healthy skin and eyes and strengthens the body’s natural defenses (immune system) against disease and infection.
However, taking too much can be harmful.
Taking too much vitamin E has been shown to thin the blood and lead to fatal bleeding.
Similarly, it may interfere with blood clotting, the body’s natural defense against excessive bleeding after injury.
Additionally, vitamin E supplementation has been linked to cancer, with one study demonstrating that taking vitamin E may increase the risk of prostate cancer in some men.
How much is safe to take?
According to the Department of Health and Social Care (DHSC), there is no harm in taking up to 540mg (800 IU) of vitamin E supplements a day.
Vitamin K
Vitamin K is a group of vitamins that the body needs for blood clotting and helps heal wounds.
Vitamin K comes in two forms: vitamin K1, which is found in green leafy plants, and vitamin K2, which is found in fermented foods such as natto and cheese.
For the general population who eat a balanced diet and take standard supplements, vitamin K toxicity is not a major concern.
“This is primarily due to the rapid utilization and short half-life of vitamin K in the body,” Taylor explained.
However, this does not eliminate the possibility of toxicity, especially in certain circumstances.
For people taking anticoagulant medications such as warfarin, taking too much vitamin K can counteract the medication and increase the risk of blood clots, the Office of Dietary Supplements (ODS) warns.
Research suggests that patients taking these drugs should keep their vitamin K intake consistent to avoid fluctuations in the effectiveness of the medication.
How much is safe to take? According to the DHSC, taking vitamin K supplements in amounts of 1mg or less a day is unlikely to cause any harm.
Vitamin B6
Vitamin B6 (pyridoxine), also known as pyridoxine, is a water-soluble vitamin that plays an important role in a wide range of physiological functions, including the storage of energy from protein.
Despite the importance of vitamin B6, there is a limit to how much your body can tolerate before experiencing side effects.
Studies have shown that exceeding this threshold can lead to toxicity known as pyridoxine-induced neuropathy, in which sensory neurons are damaged, causing numbness, pain, and burning sensations in the hands and feet, and difficulty walking.
Vitamin B6 toxicity usually occurs with long-term consumption of high dose supplements that significantly exceed the recommended daily intake, as it is rare to reach such high levels through diet alone.
How much is safe to take?
The DHSC advises not to take more than 10mg of vitamin B6 a day from supplements unless advised by a doctor.
Vitamin C
Vitamin C, also known as ascorbic acid, has several important functions.
These include:
- Protects cells and keeps them healthy
- Maintaining healthy skin, blood vessels, bones and cartilage
- Helps wounds heal
Unlike fat-soluble vitamins, excess vitamin C is typically excreted in the urine, making it relatively difficult to consume too much.
However, if consumed in extremely large amounts, it can have adverse health effects.
Studies have shown that these adverse health effects include increased levels of oxalic acid in the urine, which can lead to gastrointestinal problems and kidney stone formation.
Taking too much vitamin C can cause gastrointestinal problems such as diarrhea and, in people taking the combination drug niacin and simvastatin, may impair the body’s ability to raise high-density lipoprotein (HDL) cholesterol, warns the Office of Dietary Supplements (ODS).
This medication combines the vitamin niacin with the statin simvastatin (Zocor) and is used to treat high cholesterol.
How much is safe to take?
The DHSC says there is little harm in taking vitamin C supplements of less than 1,000mg per day.
