On the other end of the food spectrum, certain mushroom varieties are also a good source of vitamin D (PSA to vegans, vegetarians, and those who prefer plant-based items!), and are sometimes even treated with UV light to produce extra, according to the ODS. Per the USDA, morel, chanterelle, maitake, and UV-treated portabella mushrooms tend to contain the most vitamin D, although levels vary based on growing and storage conditions. For instance, chanterelle mushrooms have about 114 IU per cup.

Most of the vitamin D in the American diet, however, comes from foods that are fortified with vitamin D. Nearly all dairy milk sold in the US falls into this category, according to the ODS. (You can get 117 IU per cup of 1% milk with added vitamin D, for example.) Yogurt, plant-based milks (like soy, almond, or oat milk), cereal, and orange juice are also commonly fortified. For example, Cheerios have 60 IU of vitamin D in each 1.5-cup serving. Whatever your preference, adding in more foods that are naturally rich in vitamin D or fortified with it can help increase your intake.

3. Supplements

It’s possible to get enough vitamin D in your diet, but it’s not always easy. “If people aren’t eating a variety of foods, especially cereals, milks, yogurt, and fish, then a supplement might be needed,” Spence says.

Just a few disclaimers: It’s always smart to check with your doctor before starting a new supplement, and to do your homework before buying. If a blood test reveals a deficiency, your doctor can give you a prescription supplement or recommend an over-the-counter supplement in a dose that can restore your levels to normal, Dr. Shapses says. If you work with a registered dietitian, they may also recommend a supplement, Spence says, as well as counsel you on dietary sources of vitamin D.