It’s amazing how much we still are learning about basic nutrition. Nutritionists have long known that the nutrient beta-carotene is converted into vitamin A in the body. Beta-carotene is plentiful in colorful vegetables such as carrots and in dark vegetables such as kale, so the advice was to consume plenty of these vegetables to maintain healthy levels of vitamin A. But then, about 10 years ago, University of California–Davis researchers found that the conversion of beta-carotene to vitamin A varied considerably among people. None of the participants studied converted 100% of the beta-carotene they were given—some people converted about 30%…others, just 8%.

Now scientists have a better understanding of why this occurs. It has to do with the BCMO1 gene, which is needed to convert beta-carotene to vitamin A. New: Researchers from Newcastle University in England have found that almost half of all people studied had a variation of this gene that prevented them from efficiently converting beta-carotene to vitamin A. This means that many of you may be relying on eating vegetables to get your vitamin A but are falling short.

Too much or too little: Since you can’t be sure if you have the gene and a genetic test is not widely available, you won’t know if your genes are helping or hindering your ability to get vitamin A. Signs of vitamin A deficiency include being susceptible to respiratory or diarrheal infections. Another sign is an inability to see well at night. Vitamin A is needed to make the chemical rhodopsin, found in the retina. Without sufficient rhodopsin, it takes longer for the eyes to adjust to darkness. You can speak to your doctor about any problems you have with night vision. People who have night blindness often take as much as 10,000 international units (IU) daily of vitamin A.

One way to increase intake of vitamin A is to get it from foods such as meat (all types but especially organ meat, such as liver), cheese, eggs and whole milk. The vitamin A in these foods is provided in a form that does not need to be converted to be used, so the BCMO1 gene is not an issue. People who can’t or don’t want to get their vitamin A from animal sources can get it from a multivitamin that contains 1,000 IU to 2,500 IU of vitamin A. I recommend that pregnant women take no more than 5,000 IU daily of vitamin A. Doses higher than 10,000 IU daily have been found to cause birth defects.