Preformed vitamin A encompasses metabolically active compounds such as retinol, retinal,
Background:Vitamin A may influence gastric carcinogenesis through its essential role in controlling cell proliferation and differentiation.
You should only take the doses recommended on the product label or by your health care provider. Vitamins A, D, E and K are fat-soluble vitamins. That means they're stored in your liver and fatty tissue. If you take too much of them, you could experience vitamin toxicity, which could affect different organs.
Too much Vitamin A
Retinol is the form of vitamin A that causes the greatest concern for toxicity. If you take a multivitamin, check the label to be sure the majority of vitamin A provided is in the form of beta-carotene, which appears to be safe.
Diet – Liver is high in vitamin A. The liver of certain animals, including the polar bear, bearded seal, fish and walrus, are particularly toxic (see Liver (food) § Poisoning). It has been estimated that consumption of 500 grams (18 oz) of polar bear liver would result in a toxic dose for a human.
Acute systemic vitamin A toxicity typically arises when an individual consumes over 100,000 RAE within a short period, often from supplements or high-dose medications. The toxicity symptoms include nausea, vomiting, headache, dizziness, irritability, blurred vision, and muscular incoordination.
It was concluded that at least in some western countries chronic vitamin A consumption might represent an appreciable cause of chronic liver disease, the recognition of which mainly relies on expert liver biopsy interpretation.
Owing to their ability to accumulate in the body, fat-soluble vitamins have a higher potential for toxicity than do water-soluble vitamins. Iron-containing vitamins are the most toxic, especially in pediatric acute ingestions.
In addition, taking a supplement that contains too much vitamin D can be toxic in rare cases. It can lead to hypercalcemia, a condition in which too much calcium builds up in the blood, potentially forming deposits in the arteries or soft tissues. It may also predispose people to painful kidney stones.
Vitamin A. Vitamin A, also known as retinol, produces the pigments in the retina of the eyes. More importantly, it is a vital nutrient for the photoreceptors in your eyes, which determine vision quality in low-light conditions.
Taking more than 3,000 mcg a day of oral vitamin A supplements long term can cause: Bone thinning. Liver damage. Headache.
Vitamin A (fat-soluble): Too much can cause hypervitaminosis A, symptoms of which may include blurry vision, bone pain, decreased appetite, liver disease, high calcium levels and osteoporosis.
It is more important that people do not experience any breaks in their daily supplementation of a vitamin, especially if they are taking it to manage a deficiency.
Vitamin D/calcium supplementation together with high vitamin A and calcium/magnesium intake resulted in significant increases in lung cancer risk among current smokers.
Current research shows that vitamin B6 supplementation may increase the skin's sensitivity to UV light, thus increasing the risk of skin cancer. If you are concerned about photosensitivity and currently take vitamin B6, talk with your doctor about reducing or eliminating this supplement to see if it helps your skin.
Optimum intake
There is some uncertainty about the amounts of vitamin D a person should consume. The National Academy of Medicine recommend a daily intake of 600 international units (IU) for adults aged 19–70 years and 800 IU per day for individuals aged 70+ years.
“Biotin is essential for hair and nail growth; biotin deficiency, in fact, can lead to hair loss and brittle nails,” says Carmen Castilla, MD, a board-certified dermatologist based in New York City.
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.
Fat-soluble vitamins (like A, D, E, and K) don't get flushed out in the urine, so they're the most likely to cause vitamin toxicity. Vitamins A and E may pose the greatest risk of toxicity, since they are so commonly taken and readily available.
Combining multiple supplements or taking more than the recommended dose might raise the risk that they can cause harm, said Kitchin. To lower your risk of an overdose, try looking for a multivitamin with no more than 100% of the daily value for any one nutrient to avoid an overdose, said Kitchin.
Too Much Alcohol
Alcoholic fatty liver, which causes liver inflammation (alcoholic hepatitis), eventual scarring (cirrhosis) and even liver cancer, is a process that begins on as little as four drinks a day for men and two for women. By the time you show symptoms, your liver may be damaged beyond repair.
To avoid hypervitaminosis A, don't take more than the recommended daily allowance of this vitamin. Check the ingredients of all your medicines to be sure you are not taking vitamin A from more than one source.