A few years ago, a laboratory in the United Kingdom found that over 3 percent of blood samples contained toxic levels of vitamin D. “Most of them were from people who were taking liquid vitamin D supplements, which are very highly concentrated,” says Dr. Dr. Brewer. “Some people actually swallow them from the bottle. I think there is a perception that all vitamins are good for you and that more is better than less, which is absolutely not the case.
Dr. Brewer believes that some groups benefit from higher doses than the officially recommended 10 mcg per day, including those over age 50, for whom she prescribes 50 mcg. However, very high doses are potentially dangerous because vitamin D is fat-soluble and the body does not have a satisfactory mechanism for excreting the excess.
Dr Dwayne Mellor, senior lecturer at Aston Medical School, recommends that most people stick to the recommended 10mcg, although a maximum of 100mcg per day is generally considered safe. Some people with a diagnosed deficiency may need more, but it should only be taken under medical supervision.
“There doesn’t seem to be any real benefit to taking more unless you’re deficient,” says Dr. Mellor. He says there’s no real way to know if you’re deficient except by getting a blood test; you can ask your GP for this if you think you have symptoms, or tests are offered privately at some medical clinics. Deficiency symptoms, including stomach cramps, low mood and bone pain, develop over time.
“In the long term, very low levels of vitamin D affect your bone health because you’re not absorbing as much calcium from your food, and your body balances it out by pulling it out of your bones,” Dr. Mellor says. This can lead to conditions such as rickets in children and bone pain caused by a condition called osteomalacia in adults.
But anyone taking vitamin D supplements needs to be sure they don’t accidentally consume too much, as the way doses are measured and printed on the packaging can be confusing. The word microgram is sometimes spelled with the Greek symbol μ followed by the letter g (μg). And sometimes vitamin D strength is listed in international units (IU) rather than micrograms. Dr Mellor warns against mixing the two up: 1mcg = 40 IU, so the recommended daily intake in the UK is 400IU or 10mcg.
The maximum recommended daily limit in the UK – from diet and supplements combined – is 100mcg for adults and children 11 – 17 years; 50mcg for children 1 to 10 years; and 25mcg for infants. Be sure to include all foods such as breakfast cereals and milk, which are sometimes fortified with vitamin D.
If you decide to take supplements, vitamin D3 (cholecalciferol) is more effective than D2 (ergocalciferol), according to the NHS. And some studies show that taking a vitamin D supplement with the largest meal of the day improves absorption.
Dr. Brewer advises caution when taking other supplements, especially iron, vitamin A (especially for pregnant women), and selenium. “For them, there’s a narrow window between a dose that’s desirable and a dose that’s toxic, and it can be easy to take too much.”
In other words, when it comes to vitamins, you can certainly have too much of a good thing.
Add Comment