Non-cow’s milk beverages like soy, almond, and even omega-3-rich hemp milk, are big business, since many consumers see them as healthier alternatives to cow’s milk. These products also ease parents’ minds when their children with milk allergies or lactose intolerance crave something to pour on their morning cereal.

But as more families make the switch, say the authors of a new study, children may be unintentionally running the risk of low vitamin D levels. Vitamin D is a nutrient added to cow’s milk that is essential for maintaining strong bones. 

“Children drinking only non-cow's milk were more than twice as likely to be vitamin D deficient as children drinking only cow's milk,” said study author Dr. Jonathon Maguire, a pediatrician and researcher with St. Michael's Hospital in Toronto, Canada, in a press release. “Among children who drank non-cow's milk, every additional cup of non-cow's milk was associated with a 5 percent drop in vitamin D levels per month.”

In the study, published online today in the Canadian Medical Association Journal, researchers surveyed 3,821 healthy children between the ages of 1 and 6 about how often they drank cow’s milk and cow’s milk alternatives. More than 10 percent of the children drank non-cow’s milk beverages regularly, with the amount consumed linked to lower levels of vitamin D in the blood.

Learn About the Benefits of Vitamin D »

Cow’s Milk Fortified with Vitamin D

Vitamin D works in part by helping the body absorb calcium from food and supplements, so low levels of vitamin D in the blood can reduce the bone-building benefits of calcium in the diet. More severe cases of vitamin D deficiency can result in rickets, a softening and weakening of the bones that can also cause bone deformities.

In the early 1900s, rickets was so common in the United States that the government started a campaign to fortify cow’s milk with vitamin D. This continues to this day, with vitamin D sometimes added to certain other food products like breakfast cereal, yogurt, and orange juice. Non-cow’s milk, including goat’s milk, is also sometimes fortified, but not consistently.

"It is difficult for consumers to tell how much vitamin D is in non-cow's milk," said Maguire. "Caregivers need to be aware of the amount of vitamin D, calcium, and other nutrients in alternative milk beverages so they can make informed choices for their children."

The amount of vitamin D required daily by children — as well as by adults up to age 70 — is 600 International Units (IU) per day. A cup of fortified cow’s milk contains at least 100 IU, so a child would need to drink five to six glasses of milk a day to obtain enough vitamin D.

Some foods contain vitamin D naturally, with the highest amounts found in fatty fish like salmon and snapper. Certain deli meats, beef liver, and egg yolks can also add vitamin D to the diet, although these are not suitable for vegans or vegetarians, unless they eat eggs. Most children’s multivitamins also contain vitamin D. 

Read More: The Effects of Vitamin D Deficiency »

Catch Vitamin D from the Sun's Rays

Fortunately for us, our bodies make vitamin D whenever our skin is exposed to UV-B rays from the sun. Early human ancestors probably made enough vitamin D this way, but these days we keep the majority of our skin covered most of the time.

During the summer months most people can make enough vitamin D with just five to 30 minutes of sun exposure at least twice a week, with the best times for vitamin D production between 10 a.m. and 3 p.m. How much sun you need, however, depends on the amount of skin exposed and the pigmentation of the skin. Darker skin blocks more UV-B rays, so it can take longer in the sun for a darker skinned person to make enough vitamin D.

In the winter, it’s also harder to produce vitamin D from the sun the further north you go because the sun doesn’t rise high enough in the sky for the UV-B rays to make it through the atmosphere. In places like New York City or London, the winter sun is ineffective at producing vitamin D, but the body can survive on the stores built up during summer.

Exposure to the sun is a good way to produce vitamin D, but concern about skin cancer has parents careful about sending their children outside to play. Making vitamin D from the sun, however, only takes a few minutes of exposure each day.

To reduce the risk of skin cancer, the skin should never be allowed to burn. The American Academy of Dermatology recommends that children also stay covered up and use a sunscreen with a minimum of SPF 30.

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