We tend to think that vitamins are always a good thing, and that if one helps – then two will surely help even more. But that is not always true. Like anything good, vitamins also need to come in moderation. Dietary supplements consumed in excessive doses can cause unnecessary strain on the body, unpleasant side effects, and in some cases even real damage to internal systems.
Here are some examples and explanations:
Vitamin C
Vitamin C is considered one of the most popular vitamins, mainly thanks to its image as an immune booster and protector against colds.
It is water-soluble, meaning any excess not needed by the body is excreted in the urine – and therefore many believe it cannot be overdone. But in practice, even vitamin C, when consumed in very high amounts from supplements, can cause unpleasant symptoms and even harm.
Doses of more than 2,000 mg per day – which is twenty times the recommended daily amount – can cause diarrhea, stomach pains, gas, and digestive discomfort. Among people prone to kidney stones, excessive intake of vitamin C may increase the risk of oxalate stone formation.
A study published in JAMA Internal Medicine found a link between daily intake of vitamin C supplements and an increased risk of kidney stones in men. A constant surplus of vitamin C also creates unnecessary strain on the kidneys, which must filter and excrete it.
The reassuring news is that it is almost impossible to reach a dangerous excess from dietary sources. Vitamin C is abundant in fruits and vegetables – primarily red peppers (the richest source), citrus fruits, kiwi, strawberries, broccoli, tomatoes, and cabbage.
Consuming a balanced diet that includes fresh vegetables and colorful fruits easily provides the recommended daily amount (about 75 mg for women and 90 mg for men), without the need for supplements – unless a deficiency has been diagnosed in blood tests.
B Vitamins (especially B6)
B vitamins are an essential group of nutrients, generally considered very safe for use, especially since they are water-soluble and excess amounts are excreted in the urine. But again – not everything soluble is necessarily harmless.
Vitamin B6, also called pyridoxine, is essential for proper nervous system function, production of serotonin and dopamine, strengthening the immune system, and breaking down proteins in the body.
It sounds harmless – but when taken in excessive amounts from supplements over time, it can cause real nerve damage. A daily intake of more than 100 mg of B6 – an amount that may be found in “fortified” supplements – can lead to tingling, numbness, prickling sensations in the hands and feet, imbalance, a slight feeling of drunkenness, and sometimes even prolonged neurological damage.
A study published in Neurology found that women who took B6-rich supplements over a long period suffered more from neuropathy symptoms compared to those who consumed the vitamin only through food.
In food, however, there is no reason to worry: Vitamin B6 is abundant in many foods – both animal and plant-based – making it easy to reach adequate levels without supplements. Chicken breast, turkey, fish such as tuna and salmon, liver, and eggs provide good amounts of B6 from animal sources. In plants, it can be found in potatoes and sweet potatoes, bananas, avocados, almonds, sunflower seeds, whole grains like oats, and legumes such as chickpeas, lentils, and beans.
A daily menu that includes cooked chicken breast, a medium potato, and one banana already easily meets the daily recommendation.
Fat-soluble vitamins – this is where it gets serious
Unlike water-soluble vitamins (such as C and B), whose excess is excreted through urine, fat-soluble vitamins (such as A and D) can accumulate in the body to toxic levels, since the body has no easy way to “flush out the excess.”
Vitamin A
Vitamin A is one of the most important vitamins for vision, immune system function, and the health of skin and mucous membranes – but an excess of it, especially when consumed from supplements or animal sources like liver, can be dangerous.
Excessive intake over time can cause headaches, fatigue, dry skin, hair loss, and even liver damage.
It is important to distinguish between active vitamin A found in animal foods and beta-carotene – the plant-based source (for example in carrots, pumpkin, and sweet potatoes) – which the body converts only as needed.
Excessive consumption of carrots may cause an orange tint in the skin, especially on the palms, but will not cause poisoning – simply because the body regulates the conversion amount.
On the other hand, uncontrolled intake of pure vitamin A supplements, or frequent consumption of large amounts of beef liver, can lead to a dangerous excess.
Vitamin D
Vitamin D has gained enormous popularity in recent years – and rightly so: It is essential for bone health, immune system function, reducing inflammation in the body, and even balancing mood.
Excessive intake of it, especially from very strong supplements, can be dangerous.
Vitamin D is fat-soluble and stored in the body, so when consumed in overly high doses over time – for example, more than 10,000 International Units (IU) per day – symptoms of toxicity may appear: Nausea, vomiting, constant thirst, kidney stones, and in rare cases even impaired heart and kidney function.
A study published in the Journal of Clinical Endocrinology & Metabolism described cases of real harm from chronic intake of vitamin D supplements in higher-than-needed doses, even among people who did not previously suffer from a deficiency.
It is worth remembering that vitamin D can be obtained not only from supplements but also from moderate sun exposure, as well as from foods such as fatty fish, eggs, and fortified milk. Blood levels can be tested with a simple blood test – and only in cases of real deficiency, and according to a doctor’s or dietitian’s recommendation, should one consider a suitable supplement in the correct dosage.
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