A few years ago, a UK lab found that more than 3% of blood samples contained toxic levels of vitamin D. “Most of these were from people who had been taking liquid vitamin D supplements, which are very concentrated, ”says Dr. Brewer. . “Some people actually take them out of the bottle. I think there’s a perception that all vitamins are good for you and that more is better than less, which is not absolutely the case.”
Dr. Brewer believes some groups benefit from higher-than-officially recommended doses of 10 mcg per day, including those over 50, for whom she prescribes 50 mcg. However, very high doses are potentially dangerous because vitamin D is fat-soluble and the body has no satisfactory mechanism for excreting any excess.
Dr. Duane Mellor, a tenured professor at Aston Medical School, recommends that most people adhere to the recommended 10 mcg, although a maximum of 100 mcg a day is generally considered safe. Some people with a diagnosed deficiency may need more, but they should only be taken under medical supervision.
“There doesn’t seem to be any real benefit in taking more, unless it’s deficient,” Dr. Mellor says. He says there’s no real way to know if you’re missing it, except by doing a blood test; You can ask your GP if you think you have symptoms or if tests are privately available at some medical clinics. Symptoms of deficiency, such as stomach cramps, low mood, and bone pain tend to develop over time.
“In the long run, very low levels of vitamin D affect your bone health because you don’t absorb as much calcium from your food and your body balances it by extracting it from your bones.” says Dr. Mellor. This can lead to conditions such as rickets in children and bone pain caused by a disease called osteomalacia in adults.
But anyone taking vitamin D supplements should make sure they are not consuming too much accidentally, as the way doses are measured and printed on packaging can be confusing. The word microgram is sometimes written with the Greek symbol μ followed by the letter g (μg). And sometimes the strength of vitamin D is indicated in international units (IU) instead of micrograms. Dr. Mellor warns that the two are not mixed: 1 mcg = 40 IU, so the recommended daily intake in the UK is 400 IU or 10 mcg.
The recommended daily limit in the UK, based on diet and combined supplements, is 100 mcg for adults and children aged 11-17; 50 mcg for children 1 to 10 years; and 25 mcg for babies. Be sure to consider any foods, such as breakfast cereals and milk, that are sometimes fortified with vitamin D.
If you choose to take supplements, vitamin D3 (cholecalciferol) is more effective than D2 (ergocalciferol), according to the NHS. And some studies have shown that taking a vitamin D supplement with the biggest 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 these, there is a narrow window between a dose that is desirable and a dose that is toxic, and it can be easy to take too much.”
In other words, when it comes to vitamins, you can certainly have too many good things.