Vitamin D may be known as the sunshine vitamin, but according to a new survey by Prevention and supplement company Centrum, few of us think to look for it in the fridge—and that's a big mistake.

"The sun is not strong enough for the body to make vitamin D from October to May, especially for those living north of Atlanta," says Althea Zanecosky, RD, a spokesperson for the American Dietetic Association. That's probably why nearly half of people tested at winter's end were low on vitamin D, according to a University of Maine study.

Compounding the problem is our vigilant use of sunscreen; SPF 15 blocks 93% of UVB rays, the type our bodies use to make D. Skin also has a harder time producing vitamin D with age. All this adds up to a big problem, as evidence continues to mount that the vitamin, long associated with bone health, also helps to regulate the immune system, lower blood pressure, protect against depression, and reduce risk of type 2 diabetes, high blood pressure, and several kinds of cancer. A 2014 study from the University of California-San Diego School of Medicine also found that people with low vitamin D levels were twice as likely to die prematurely. 

So are you getting enough D? Probably not. The Institute of Medicine has set the Recommended Dietary Allowance (RDA) of vitamin D at 600 international units (IU) for everyone under the age of 70. (It's 800 IU for adults 70+.) But many experts believe that's too low. "There is talk that the RDA may be increased," says Zanecosky. "Many physicians are now advising 2,000 millagrams daily for those with low blood levels."

Many respondents in the Prevention and Centrum recent nutrient survey were rightfully concerned they weren't getting enough D, with 22% actively looking for it in foods. But just 9% knew that salmon is a good natural source of the vitamin, and only 5% recognized fortified tofu as one, too. Here are some other ways to get more in your diet:

Wild-caught fish
(425 IU in 3 oz salmon, 547 IU in 3 oz mackerel)

Beef or calf liver
(42 IU in 3 oz)

Egg yolks
(41 IU per egg)

Canned fish
(154 IU in 3 oz tuna, 270 IU in 3.5 oz sardines)

Shiitake mushrooms
(40 IU in 1 cup)

Milk: whole, nonfat or reduced fat
(100 IU in 8 oz)

Yogurt
(80–100 IUs in 6 oz)

Almond milk
(100 IU in 8 oz)

Pudding made with milk
(49-60 IUs in ½ cup)

Orange juice
(137 IU in 1 cup)

Breakfast cereals
(50–100 IUs in 0.75–1 cup)

Fortified tofu
(80 IU in 3 oz)

Oatmeal
(150 IU in 1 packet)

Cheese
(40 IU in 1 slice)