Ask people about the essential nutrients in milk and the top answers are calcium and Vitamin D. (Sadly, many consumers don't think of milk as a significant source of protein - we've got work to do as an industry to change that.)
We all know the story behind Vitamin D in milk. In the 1930s, milk processors, working together with government health officials, began fortifying fluid milk with Vitamin D to prevent rickets in children. Rickets is a weakening of the bones caused most often by Vitamin D deficiency.
Vitamin D's main role in the body is to facilitate absorption of calcium and phosphorous (two of the main minerals needed for bone health) in the intestines. With Vitamin D-fortified milk, every dose of calcium and phosphorous comes with a dose of Vitamin D. As a result of fortification, the prevalence of rickets decreased considerably. Sadly, though, the number of cases of rickets has risen in recent years due, in part, to reduced fluid milk consumption.
But Vitamin D also works in other ways in the body. Recent research has shown potential links between Vitamin D levels and diabetes, high blood pressure, certain cancers, and immune system function. Large scale studies to confirm these findings are still underway. There are links, too, between Vitamin D levels and depression, but how Vitamin D works in the brain isn't yet fully understood. The bottom line is, as we learn more, Vitamin D is probably not going to become any less important.
So how do we make sure we're getting enough Vitamin D?
Most people don't have to worry. Three to four servings a day of Vitamin D-fortified foods, like milk, meet most people's needs.
We can also bolster our Vitamin D levels through exposure to sunshine. But the skin can only make Vitamin D if it's not slathered in sunscreen or buried beneath layers of Cuddl Duds and Carhartts.
But what if you don't drink fortified milk?
That was the question I asked my doctor back in the winter of 2012 after a blood test showed that my Vitamin D level was deficient.
Since we get our milk straight from the bulk tank, the milk we drink is unfortified. And, during the winter, I'm certainly not getting adequate Vitamin D from sun exposure.
Questioning Vitamin D levels also makes sense for people who tend to eat more cheese and yogurt and drink very little fluid milk, since cheese is almost never fortified and yogurt is only sometimes fortified.
My doctor recommended a Vitamin D supplement and that my Vitamin D level be checked again in six months.
What I've found is that my Vitamin D level varies during the year. In the winter, I tend to be deficient. In the summer, when I'm outside a lot in shorts and tank tops (and, no, I don't usually wear sunscreen when I'm working on the farm), my Vitamin D levels climb. So, in the summer I reduce the amount of Vitamin D supplement I take.
My doctor also recommended Vitamin D drops for Monika and Daphne when they were exclusively nursing. (We had a different doctor when Dan was a baby). The American Academy of Pediatrics agrees with this recommendation.
A word of caution, though, about Vitamin D supplementation: The entire medical community does not agree on how much Vitamin D adults and children need each day. Plus, it's possible to consume too much Vitamin D.
If you don't drink fortified milk or get adequate sun exposure, consider asking your doctor about Vitamin D at your next check-up.
References available upon request.