Tuesday, March 23, 2010

Vitamin A Toxicity

Vitamin A toxicity becomes an issue when the intake is about ten times the recommended daily amount (the RDA is 900 micrograms for male adults). The tolerable upper limit is about 3000 micrograms per day. More than this amount of vitamin A during pregnancy can cause birth defects and spontaneous abortion. The most notable birth defects in pregnancy are cardiac ones. That is one of the reasons why the formulations of pre-natal vitamins have changed in the past years. There used to be only retinol (active form of vitamin A) in pre-natal vitamins, but they now removed some of that and replaced it with beta-carotene (not active but can be converted to vitamin A in the body).

It can cause blurred vision and painful swelling of the long bones, like the femur or the leg. There can be swelling of breast tissue in men, called gynecomastia. However, the major cause of gynecomastia in men is obesity. Impotence and other sexual dysfunction can also occur with a level of vitamin A that is outside the recommended range.

There can be calcium loss in bones that can lead to osteoporosis. It can cause irritability, nausea, headache, fatigue, dizziness and diarrhea. Skin and hair change. Skin itches, becomes oily and hair falls. In infants, it can cause an abnormal softening of the skull bone and weight gain.

A consequence of excess beta-carotene, which is much less likely to be toxic than pre-formed retinol, is a yellow or orange skin. I knew someone who loved carrots so much that had bags of them every day. His hands and feet had a nice orange blow to them. Maybe this is not the look you are going for, but still gives a nice glow to your skin.

Is it harmful to eat a lot of carrots? No. Keep in mind that the studies designed to test the toxicity of a certain vitamin always use supplements and not real food. There is a difference between beta-carotene you get in your food and the one you take as a supplement. In some studies individuals were having up to 25000 micrograms of beta-carotene. You’re unlikely to reach that amount with carrots.

You’re not going to have an adverse outcome from food, but from supplements it is possible.

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