If you drink milk, chances are you don’t stop to read the label before pouring a glass. Milk is made of, well, milk, right? Not completely. If you take a look at the list of ingredients, you’ll see vitamin D is listed, even if the milk isn’t advertised as being fortified with the vitamin.
Why? The answer is simple, really—rickets. The childhood bone disorder is caused by not getting enough vitamin D. In the 1900s, it affected many children, including 80 percent of kids living in Boston. Around this same time, scientists learned that milk’s minerals, like calcium, played a role in bone and teeth development and a doctor discovered that vitamin D was needed to help calcium get absorbed—and therefore prevent rickets.
“Rickets became an epidemic as you had the Industrial Revolution and with it, childhood labor,” Patsy M. Brannon, from the division of nutritional sciences at Cornell University, told HuffPost. Childhood labor meant children were working and simply not exposed to enough sun.
While the sun is in fact the best way to get vitamin D, it’s not without its own risks, and because vitamin D isn’t found in many foods, fortifying milk was a pretty easy solution. It is thanks to this fortification that rickets is now a fairly rare disease in the United States.
The National Institute of Health Office of Dietary Supplements recommends daily intake of vitamin D should be 600 IUs for men and women between the ages of 1-70. (It increases to 800 after 70.)
If you’re not a dairy milk drinker, there are other ways to get your vitamin D. Most almond milks are also fortified with the vitamin, as are cereals and orange juice. Small amounts are also found in eggs, cheese and some mushrooms, but the most vitamin D-rich foods are some you may not want to eat—like cod liver oil, sardines and caviar. We’ll stick to our milk, thank you!
Turns out it’s not just milk that “does the body good,” but actually vitamin D we can all thank for our healthy bones!
This story originally appeared on Simplemost. Checkout Simplemost for other great tips and ideas to make the most out of life.