Any ingredient in a multiple vitamin supplement can be toxic in large amounts, but the most serious risk comes from iron or calcium. Additional risks are associated with large or toxic doses of calcium, vitamin D, and vitamin A.
Dwyer says vitamin D, calcium, and folic acid are three nutrients you may get too much of, especially through supplements. Adults who regularly far exceed the 4,000 international units (IUs) daily safe upper limit for vitamin D might may end up with serious heart problems.
Megadoses of vitamins A, D, E or K can be toxic and lead to health problems.
Extra amounts of water-soluble vitamins are typically excreted. The fat-soluble vitamins A and D are the most likely to cause toxicity symptoms if you consume them in high amounts.
Safety and side effects
While the recommended daily amount of vitamin B-12 for adults is 2.4 micrograms, higher doses have been found to be safe. Your body absorbs only as much as it needs, and any excess passes through your urine.
The upper limit for all adults is 2,000 mg a day. Although too much dietary vitamin C is unlikely to be harmful, large doses of vitamin C supplements might cause: Diarrhea. Nausea.
An excess of B6 can cause nerve damage, while excess quantities of vitamin B12 -- while rare -- may cause complications for people with certain underlying conditions. Consult your doctor before taking vitamin B6 or vitamin B12 to avoid health problems.
Heat, light, exposure to air, cooking in water and alkalinity are all factors that can destroy vitamins.
Large quantities of the fat-soluble vitamins can be stored in the liver and in adipose tissue, and toxicity can result following excessive intake of vitamins A and D. Vitamins E and K are generally considered nontoxic.
You can—but it's probably not a good idea. For some supplements, optimal absorption can depend on the time of day taken. Not only that—taking certain vitamins, minerals, or other supplements together can also reduce absorption and may result in adverse interactions, which can be harmful to your health.
Don't use calcium, zinc, or magnesium supplements at the same time. Also, these three minerals are easier on your tummy when you take them with food, so if your doctor recommends them, have them at different meals or snacks.
The main consequence of vitamin D toxicity is a buildup of calcium in your blood (hypercalcemia), which can cause nausea and vomiting, weakness, and frequent urination. Vitamin D toxicity might progress to bone pain and kidney problems, such as the formation of calcium stones.
Signs of too much zinc include nausea, dizziness, headaches, upset stomach, vomiting, and loss of appetite. If you take too much zinc for a long time, you could have problems such as lower immunity, low levels of HDL ("good") cholesterol, and low copper levels.
Vitamin B6 – Another important nutrient co-factor involved in numerous biochemical pathways in the body, including the modulation of adrenal gland activity and the stress response, and since stress also depletes vitamin B6, higher intakes are required when stressed.
There is some contention in the medical community on which vitamin is actually most important for your body. The common consensus says it's either Vitamin B12 or Vitamin D. While both deserve to be in the tops slots, We're going to call it with Vitamin D, simply because so many people are deficient.
Water-soluble vitamins (vitamin C and the B-complex vitamins, such as vitamin B6, vitamin B12, and folate) must dissolve in water before they can be absorbed by the body, and therefore cannot be stored. Any water-soluble vitamins unused by the body is primarily lost through urine.
Vitamin C is a water-soluble and temperature-sensitive vitamin, so is easily degraded during cooking, and elevated temperatures and long cooking times have been found to cause particularly severe losses of vitamin C [12].
B-complex vitamins and vitamin C are water-soluble vitamins that are not stored in the body and must be consumed each day. These vitamins can be easily destroyed or washed out during food storage and preparation.
You're unlikely to get too much vitamin B complex from your diet. That's because B complex vitamins are water soluble. That means they aren't stored in your body but are excreted in your urine daily. You're also unlikely to get too much vitamin B if you're taking any supplementation as directed.
Although folate or folic acid are forms of water-soluble B vitamin, excessive levels in the system can lead to a lot of side effects. Common signs of folic acid overdose include gastric problems like bloating, diarrhoea, abdominal cramps, nausea and gas.
When a higher dose of vitamin B is taken, people may suffer from indigestion, nausea or mild diarrhea. People with a prior history of gastrointestinal problems and aged individuals are more likely to suffer from intense stomach cramps and severe diarrhea after taking high doses of vitamin B.
Overdose. Signs of a magnesium overdose can include nausea, diarrhea, low blood pressure, muscle weakness, and fatigue. At very high doses, magnesium can be fatal.