Vitamin D3 in and of itself is not a toxic substance; it is actually a very beneficial fat-soluble vitamin, required for numerous bodily functions. However, according to Elson Haas in his book "Staying Healthy with Nutrition," vitamin D intake must be more finely tuned with regards to the right therapeutic dosage than most other vitamins, and an overdose can indeed be quite toxic.
Sources of D3
Your body makes vitamin D3 when your skin is exposed to sunlight. Haas believes that an overdose of D3 may be a contributing factor to sun poisoning symptoms. Vitamin D3 is also found in small amounts in animal foods such as egg yolks, butter, liver and the oily fish mackerel, sardines, salmon and herring. In addition, it can be derived from animals and taken as a supplement. An overdose of supplemental D3 is perhaps the most common cause of D3 toxicity.
Why Excess D3 Can Cause Toxicity
The main reason why D3 poses a greater threat for toxicity than many other vitamins is because it is a fat-soluble vitamin. This means that unlike water-soluble vitamins that are excreted in sweat and urine when there is a surplus intake, excess vitamin D3 gets stored in your body's tissues. If you take too much D3 regularly, then it will begin to accumulate in your body, and this accumulation can eventually lead to toxicity. Unfortunately, since vitamin D stores itself in fat, vitamin D intoxication can persist for weeks after vitamin D ingestion is terminated.
Suggested Intake
According to the PDR for Nutritional Supplements, the recommended daily allowance, or RDA, for vitamin D is currently set at 400 international units. Pregnant women are advised not to exceed this amount. Many health care professionals believe this to be too low for most individuals, however, and the PDR says that doses of up to 2,400 IU a day in healthy individuals rarely causes any adverse reactions. However, a long-term intake exceeding 3,700 IU a day may cause toxicity.
Symptoms of Toxicity
Symptoms of mild vitamin D toxicity include excessive thirst, diarrhea, nausea and headaches. More research needs to be done, but there may also be a link between long-term excess vitamin D intake, high blood pressure and atherosclerosis, according to Haas. Finally, too much D3 can lead to abnormal calcification of soft tissue and hypercalcemia, a condition in which there is too much calcium in the blood.
Super Doses and Hypercalcemia
Symptoms of hypercalcemia in its early stages include nausea, weakness, headache, vomiting, dry mouth, constipation, muscle pain, metallic taste and bone pain. If hypercalcemia progresses, anorexia, kidney problems, weight loss, insomnia, conjunctivitis, pancreatitis, hyperthermia, decreased libido, hypertension and cardiac arrhythmias may all ensue. Hypercalcemia typically only occurs in individuals taking prescribed super vitamin D doses of 50,000 to 200,000 IU daily. Everyone's vitamin D requirements are different; to prevent toxicity, you should talk to your health care practitioner before supplementing with D3.
References
- "Staying Healthy with Nutrition"; Elson M. Haas, MD; 2006
- PDR for Nutritional Supplements; "Vitamin D"; Sheldon Saul Hendler; 2001
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