Vitamin D is an important vitamin used by our bodies to assist in the absorption and use of the bone-building mineral calcium. Persons that are deficient in vitamin D are at greater risk of having bones that are soft, weak, or misshapen. Emerging evidence is also suggesting that vitamin D may play an important role in other bodily processes, including modulating cell growth, boosting the immune system, and reducing inflammation.

Our bodies obtain Vitamin D in three ways. The most common is for our bodies to make it from a substance that our skin produces after it is exposed to the sun’s ultraviolet (UV) B rays. However, several factors can interfere with this process. One is the use of sunscreen, which blocks UVB rays from reaching our skin. Another is the onset of winter, a time when the sun’s rays are weaker, there are fewer daylight hours, and more of our skin is covered by bulky clothing.

In the absence of sunlight, our bodies must obtain vitamin D from either dietary supplements or certain foods. In the case of supplements, my preference is take them only under a doctor’s supervision, since taking too many risks vitamin toxicity and other negative side effects. Supplements can also interact with other medications.

That leaves food. Only a few foods are naturally high in vitamin D. These include cod liver oil and the flesh of fatty fish such as tuna, salmon and mackerel. Others, such as eggs and shiitake mushrooms, also have vitamin D but to a much lesser extent.

Some foods are fortified with vitamin D (meaning that vitamin D has been added to them before being sold to the public). These are primarily liquid and powdered milk, some fruit juices such as orange juice, and many ready-to-eat cereals. Interestingly, most dairy products made from milk, such as yogurt and cheese, are not fortified with vitamin D. (To determine whether a dairy product has been fortified with vitamin D, check its list of ingredients for either “Vitamin D2,” which is derived from plants, or “Vitamin D3,” which is derived from animals.)

Not surprisingly, neither cod liver oil nor sugary ready-to-eat cereals are on my go-to list for upping my family’s intake of vitamin D. And while I am partial to fatty fish such as salmon and tuna, eating those fish on a frequent basis would entail a significant hit to my wallet.

Milk, on the other hand, is something that is both relatively inexpensive and can be incorporated into a variety of dishes my family likes. Our weekend breakfasts frequently include pancakes or waffles made with fluid milk and occasionally a few tablespoons of powdered milk. Lunches and dinners may include scalloped potatoes, a slice of quiche, or some version of pasta with bechamel sauce (macaroni and cheese being the classic example), all of which I make using milk rather than the typically unfortified half-and-half or cream. On the rare occasions when we eat dessert, I may opt for a milk-based one such as pots de crème or, if I’m feeling especially ambitious, some homemade ice cream.

The critical factor in ensuring that all of these foods are vitamin D-rich is to make them from scratch or mostly from scratch using vitamin D-fortified fluid or powdered milk. Store-bought versions of these items, especially those that start out in boxes or come from the frozen food section of your grocery store, are unlikely to be made from milk or milk products that were fortified with vitamin D.

Finally, if you are using a plant-based milk instead of cow’s milk, you should always check its ingredients to ensure that it has been fortified with vitamin D. A 2014 Canadian study found that children who drank non-cow’s milk were more than twice as likely to have insufficient levels of vitamin D than children who drank cow’s milk.