Maybe you need to get out more. The body makes vitamin D in sunlight. Just 10-15 minutes several times a week could do it. But don’t overdo it. Too much time in the sun can raise your risk of skin cancer. And there are some other catches, too.
Your age, skin color, the time of year, and where you live can make it harder to make vitamin D. So can sunscreen.
Add fortified cereals, juices, and milks (including almond, soy, rice, or other plant-based milks, as well as low-fat dairy) to your diet. And ask your doctor if you need a vitamin D supplement.