Perhaps you’ve heard this before – that many of us are deficient in Vitamin D, and that this deficiency rises during the wintertime as our exposure to sunlight is reduced. Yes, it is true that approximately 40 percent of adults in the US are vitamin D deficient. And since sunlight on our skin produces this important nutrient, we are seasonally challenged to maintain recommended levels this time of year. The good news is that we can naturally raise vitamin D levels with our eating habits, specifically by consuming enough seafood.
First, let’s examine the role that vitamin D plays in our overall health. Vitamin D is central to our ability to build and maintain good bone structure. Vitamin D absorbs calcium from our diet, and uses it to build bones and keep them strong and healthy. Vitamin D also blocks the release of parathyroid hormone, a hormone that reabsorbs bone tissue which makes bones thin and brittle. Vitamin D may also play a role in muscle function and the immune system. There are study results that suggest that it may also help prevent some cancers and diseases, although many of these results are considered either preliminary or debatable at this point in time, and further long term research is needed. But the fundamental importance of vitamin D as a builder and protector of bones throughout our lifetime is well-established.
Think of your bones as a living, changing things. Your bones cells are constantly being replaced at a rate such that you effectively have a whole new skeleton every decade. Vitamin D plays a vital role in this constant replenishment of bone. A deficiency in D can cause problems ranging from Ricketts disease to osteoporosis. How much vitamin D do we need? The recommended minimum daily allowance from the Institute of Medicine is 600 IU (international units), and the safe upper limit was recently raised to 4,000 IU.
Face time in the sun is the main way most of us get our vitamin D. UV light from the sun, highest during the most intense hours between 10am and 3pm, is converted by our skin to vitamin D. If you avoid the sun, or cover up with clothing or sunscreen, you may be deficient. This time of year, our vitamin D rates generally fall in the northern hemisphere due to low light and staying indoors. There are two other ways we can increase vitamin D rates: by eating foods containing vitamin D, or taking a supplement. Fish, along with egg yolks, are among the few foods naturally containing vitamin D in amounts that can provide what we need. Other foods like flour, orange juice, and milk products may contain added vitamin D. Eating fish two or three times per week is a great way to help you receive the steady amount of vitamin D that you need for good bone health.
One current area of scientific interest, where vitamin D has been cited as possibly playing a key role, is the interrelationship between human dietary habits, nutritional intake, and sleep quality. In one recent study (J Clin Sleep Med 2014;10(5):567-575), 95 men in the US ranging in age from 21 to 60 were assigned either a Fish diet containing 3 salmon meals per week or a Control diet that contained poultry, beef or pork. This study was run from September to February in an inpatient facility. Sleep (amount of time it takes to fall asleep, actual sleep time, and actual wake time), self-perceived sleep quality and daily functioning, as well as patients’ vitamin D status, EPA+DHA, and heart rate variability, were assessed pre- and post-diet. The study concluded that fish consumption appeared to have a positive impact on sleep in general and also on daily functioning, which may be related to vitamin D status and heart rate variability. Fish consumption throughout the winter had a positive effect on EPA+DHA levels and resting heart rate variability, and post-study the vitamin D status in the Fish group was closer to the level considered optimal compared to the Control group.
Vitamin D, because of its role in proper bone formation, is a fundamentally important nutrient for all of us. Additionally, it is clear that scientists are just starting to discover other important roles that Vitamin D may play in our lives, including sleep, mood and other facets.