Non-cow's milk - such as rice, almond, soy and goat's milk - have become increasingly popular due to their perceived health benefits or because of milk allergies and lactose intolerance. However, a new study suggests that children who drink such beverages have lower blood levels of vitamin D, compared with those who drink cow's milk.
The researchers - led by Dr. Jonathon Maguire from St. Michael's Hospital in Toronto, Canada - publish their findings in the Canadian Medical Association Journal (CMAJ).
They note that although parents may choose non-cow's milk drinks for their children because of potential health benefits, whether they offer health advantages over cow's milk is unclear.
Though it is possible to fortify non-cow's milk beverages with vitamin D, this is voluntary in both countries, where little regulation on fortification of such beverages exists.
According to the National Institutes of Health, vitamin D maintains strong bones by helping the body absorb calcium from food and supplements. Individuals who are vitamin D deficient can develop soft, thin, brittle bones - known as rickets in children and osteomalacia in adults.
Because very few foods naturally contain vitamin D, fortified foods provide most of the vitamin D in the American diet.
'Children may also be at risk of reduced calcium intake'
To further investigate how consumption of non-cow's milk might affect vitamin D levels in children, the researchers assessed differences in vitamin levels in 2,831 healthy children between the ages of 1-6 years old, who consumed cow's milk or alternative milk drinks.
- Muscles need vitamin D to move, and nerves need it to carry messages between the brain and every body part
- The immune system needs vitamin D to fight off bacteria and viruses
- Though few foods naturally contain vitamin D, fatty fish - including salmon, tuna and mackerel - are among the best sources.
The children were all recruited from seven pediatric or family medicine practices in Toronto, Canada, and of these children, 85% drank cow's milk, while 12% drank non-cow's milk. The other 3% had unknown milk consumptions.
Results show that children who only drank non-cow's milk were more than twice as likely to have a 25-hydroxyvitamin D level below 50 nmol/L, compared with children who drank only cow's milk.
The researchers explain that normal vitamin D levels are 50-150 nmol/L and higher. Additionally, among children who drank both milk types, the team found that each additional cup of non-cow's milk consumed was linked to a decrease in 25-hydroxyvitamin D level.
"Our findings may be helpful for health care providers caring for children who drink non-cow's milk beverages because of an allergy to cow's milk, lactose intolerance or a dietary preference," write the authors, adding that better "education regarding nutrition labels is important to ensure that non-cow's milk products fortified with vitamin D are being chosen by parents and caregivers."
In a linked editorial to the study, Drs. Sina Gallo - of George Mason University in Virginia - and Celia Rodd - of Children's Hospital in Winnipeg, Canada - note that attention needs to be paid to what types of beverages children are consuming and their vitamin D content.
"Moreover," they write, "with the exception of goat's milk, beverages not fortified with vitamin D will also likely not contain calcium. If parents do not understand this connection, children may also be at risk of reduced calcium intake."
Though their study had a large sample size, the researchers report a few limitations, including its cross-section design, which makes causality unable to be determined.
Additionally, the parent-reported measurements of children's milk consumption mean that the data could have been affected by recall bias.
Another major limitation of the study is that the children all had lighter skin pigmentation and higher vitamin D supplementation than non-participants, which means the findings "may not be generalizable to children from other urban areas or from nonurban areas who may be at higher risk of vitamin D deficiency."
Commenting on the vitamin D levels observed in the study, Drs. Gallo and Rodd write:
"Although cow's milk and non-cow's milk beverages are not necessarily created equal, it is fortunate that few of the young children assessed by Lee and colleagues were deficient in vitamin D regardless of the beverages consumed.
This may reflect concurrent use of vitamin D supplements, or a generous estimated average requirement for vitamin D (the amount that meets the needs of 50% of the population)."
The study authors conclude that the "take-home message from this important study is that all of us - health professionals and consumers - must be well informed about food fortification practices to ensure compliance with current recommendations."