The human body requires 13 vitamins, which are organic compounds, for various biochemical reactions. Most are water-soluble, but four are considered fat-soluble and include vitamins A, D, E and K. Fat-soluble vitamins are absorbed through the intestines with the help of lipids. Because fat-soluble vitamins are more stable within food and more likely to accumulate in the body's fatty tissues, they are more likely to lead to hypervitaminosis and create side effects.
Hypervitaminosis A
Vitamins in recommended dosages do not cause side effects because they are essential nutrients needed by the body. In large doses, however, fat-soluble vitamins are capable of causing side effects. Overdosing on vitamins, or hypervitaminosis, is very rare from consuming food, but more likely from vitamin supplementation, especially in those who "mega-dose."
Hypervitaminosis A occurs when the maximum limit of retinoid storage is exceeded in the liver. The excess retinoids spill over into the bloodstream and cause systemic toxicity. According to the Institute of Medicine, the lowest observed adverse effect dosage for vitamin A is 21,600 IU (Reference 2). Most supplements have 10,000 IU or less per capsule.
The symptoms of acute hypervitaminosis A include nausea, vomiting, headaches, dizziness, blurred vision, and reduced muscle control. Vitamin A causes cells to swell with fluid, so an overdose can lead to cellular rupturing. Toxicity can be reversed through intake of vitamin E, cholesterol, zinc, taurine and calcium.
Vitamin D
One form of vitamin D, cholecalciferol or D3, is produced by the skin in response to sunlight and cannot cause overdose symptoms. Hypervitaminosis D is very rare, but can occur with mega-dosing vitamin D2. Acute overdose of vitamin D2 requires between 600,000 and 1,680,000 IU per day over a period of several weeks, with a safe intake level determined at 10,000 IU per day.
The symptoms of acute hypervitaminosis D include nausea, vomiting, dehydration, decreased appetite, irritability, constipation and fatigue. Large excesses of vitamin D can cause high blood concentrations of calcium, which can lead to calcification of the soft tissues, heart and kidneys. Kidney stones and hypertension can also result. Toxicity can be reversed through a low calcium diet combined with corticosteroid drugs.
Vitamin E
According to The Merck Manuals, many adults take relatively large amounts of vitamin E for months to years without any apparent harm, although a few studies suggest that an increase in risk of hemorrhagic stroke and congestive heart failure is possible. Very occasionally, muscle weakness, fatigue, nausea and diarrhea occur in those who mega-dose vitamin E. For those on blood thinners, such as coumarin or warfarin, 1,000mg per day or more of vitamin E can increase the risk of internal bleeding.
Vitamin K
Vitamin K is important for the process of blood clotting, but the limits of toxicity have not been determined. The Merck Manuals state that vitamin K is not toxic even if taken orally in large doses, although there may be complications with increased coagulation in patients taking the blood thinner, Warfarin.
References
- "The Vitamins - Third Edition"; Gerald F. Combs; 2007
- Institute of Medicine: "Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc"; Food and Nutrition Board; 2001
- "American Journal of Clinical Nutrition"; Risk assessment for vitamin D; J.N. Hathcock et al; January, 2007
- The Merck Manuals: Vitamin E
- The Merck Manuals: Vitamin K
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