It shouldn’t be too difficult to get enough vitamin D—after all, unless you have specific liver or kidney problems that interfere with the process, your body makes it all by itself just by being in the sun.

However, new research is suggesting that vitamin D deficiency is a growing problem.

Last month, the Archives of Pediatrics & Adolescent Medicine published a study on vitamin D deficiency in otherwise healthy infants and toddlers. Researchers studied 380 children seen for routine health visits at the Children’s Hospital Boston Primary Care Center—44 of the participants were vitamin D deficient, 146 had levels “below an acceptable optimal threshold,” and one child had signs of rickets.

In a recent USA Today article, Catherine Gordon, director of the bone health program at the hospital in the study, summarized the study’s findings succinctly: “Vitamin D deficiency is much more of a health problem than anyone realized,” she says in the story.

Or, perhaps we’re just now noticing the problem.

“It is more likely that poor vitamin D status has been with us for a long time and is not being recognized more often,” says Mary Ann Johnson, national spokesperson for the American Institute of Nutrition and the Bill and June Flatt Professor of Foods and Nutrition at the University of Georgia. “If (the deficiency) is growing a bit, the main reasons are probably getting less sunshine than in the past as children play inside rather than outside quite often, and drinking less vitamin-D fortified milk.”

The solution seems simple: be outside and eat food that has vitamin D in it (most sources of vitamin D are meat and dairy, but vegans can eat fortified foods or take supplements).

So, what’s the problem?

How much vitamin D do we need, and what’s it for, anyway?
There are slightly different figures floating around for the recommended vitamin D intake.

The Food and Nutrition Board at the Institute of Medicine of The National Academies (formerly the National Academy of Sciences) recommends 200 international units (or 5 micrograms) a day for many people—that covers from birth to 50 years, and includes pregnant and lactating women. People between the ages of 51 and 70 need 400 IU (or 10 micrograms), while adults 71 or older need 600 IU (15 micrograms).

The FNB still maintains these figures, even though the American Academy of Pediatrics has recently issued recommendations for larger doses of vitamin D in children: 400 IU a day.

Vitamin D is needed for bone growth; without it, bones become thin, brittle or misshapen, causing rickets in children and osteomalacia in adults. Recently, the Journal of the American Medical Association published a study reporting that vitamin D deficiency is linked to an increased risk of death from cardiovascular disease.

Who is at particular risk for vitamin D deficiency? According to the National Institutes of Health, the list includes: breastfed infants (more on that later), adults aged 50 and older, people with limited sun exposure, people with dark skin (greater amounts of melanin reduce the skin’s ability to produce vitamin D from sun exposure), people with fat malabsorption and people who are obese. The only way to find out whether you are vitamin D deficient is to have a blood test at your physician’s office—be sure to ask for the 25-hydroxyvitamin D test, says Johnson.

The good news is that vitamin D deficiency is easy to correct, adds Johnson. It’s simple as taking a multivitamin—and that’s what she recommends doing rather than sunscreenless sunshine.

Here comes the sun…everyone hide!
We’ve all heard of ultraviolet B rays, but it’s always been as something to avoid—excessive amounts cause sunburn, chronic eye problems and skin cancer. Yet UVB rays are exactly what your body needs to make convert inactive vitamin D to active vitamin D.

Both children and adults have become sedentary and stay glued to television and computer screens, says Dr. Becky Laird, a nutritionist and chiropractor in Athens, Ga. “We don’t go out into the sun, and when we do, we put on sunscreen, and sunscreen blocks the rays that help you convert vitamin D,” she says.

Yet any dermatologist will tell you to cover up with sunscreen. In fact, the American Academy of Dermatologysays to get your vitamin D from a healthy diet rather than seeking out the sun.

Indeed, “We don’t recommend for anyone to get any more exposure than they have to,” says Dr. George Miller, a dermatologist in Athens, Ga. “Sun damage is constantly accumulating.”

“Most people get enough incidental sun exposure during their daily activities to meet their vitamin D requirements,” says the AAD in an official statement concerning vitamin D and sun exposure. And you only need brief exposure: “For a fair-skinned person in Boston or New York, at noon in June, it is 2-5 minutes.”

Just 10 minutes in the sun gives you 25,000 IU of vitamin D, says Laird.

Dr. Joyce Thomas, another dermatologist in Athens, suggests spacing out exposure in short segments throughout the day, and notes that you can get sufficient amounts of vitamin D in partial shade (even while riding in the car).

Keep in mind, though, that geography plays a role in the amount of vitamin D you can get from the sun. The NIH offers a handy example: draw a line between California and Boston: that’s 42 degrees north latitude, and if you live above it, chances are you aren’t getting enough vitamin D from being outside in the winter. If you live below 34 degrees north (that’s a line between California and South Carolina), you are likely fine for vitamin D throughout the year.

Now, time to think about food.

Watch what you eat
“Children just don’t eat things that have a lot of vitamin D in it,” says Laird. Gone are the days of regular doses of cod liver oil, she says. Plus, “the diet of most children today is pretty deplorable—not only not being nutrient-dense, but robbing the body of nutrients,” she adds, referring to high-carb and high-sugar junk food.

According to the NIH, vitamin D is present in just a few foods—mostly fish like salmon, tuna and mackerel, though it is also in fish liver oils, beef liver, cheese and egg yolks, and some (surprise!) mushrooms. In fact, says the NIH, most people get their vitamin D from fortified food like cow’s milk, soy milk, breakfast cereal, yogurt and some brands of orange juice.

Breastfeeding: is it enough?
In the Boston study, infants who were exclusively breastfed had higher rates of vitamin D deficiency. The American Academy of Pediatrics says that “human milk does not contain enough vitamin D to prevent rickets,” and suggests giving multivitamin drops within the first two months of life until they are weaned to either formula or cow’s milk. The NIH says that “prolonged exclusive breastfeeding without the AAP-recommended vitamin D supplementation is a significant cause of rickets, particularly in dark-skinned infants who are not vitamin D replete.”

Say what? We’re told that breastmilk is the perfect food for babies—so why would it be lacking in something like an important vitamin? (And not all pediatricians prescribe vitamin drops across the board.)

Here’s a reassuring thought: “Exclusively breastfed healthy, full-term infants from birth to six months who have adequate exposure to sunlight are not at risk for developing vitamin D deficiency or rickets,” says a 2003 release from La Leche League. “Rickets occurs because of a deficiency in sunlight exposure, not because of a deficiency in human milk.”

So, don’t stop breastfeeding to get your child’s vitamin D—but do take a look at both of your diets. And go play outside!