Why do we get the sniffles during the winter? We all know that colds and the flu are caused by viruses, but they seem to pop up a lot during the winter months. As a dietetic student I often get the following question, “What do I eat when I have a cold?” The first thing that pops into my head is the old saying, “Don’t eat dairy because it makes the phlegm worse.” Is there any truth to this expression? Besides increasing my vitamin C consumption is there anything I can do to make sure I get better faster?
Dairy products are a rich source of vitamin D. Vitamin D is not only important for maintaining bone health, but as research continues to discover, vitamin D does a lot more. One thing we do know is that Vitamin D is necessary for the maximum absorption of calcium. Calcium is the most widely used mineral in our bodies. We need calcium for a variety of reasons. Calcium channels are necessary for nerve function, muscle function, insulin release, signal transduction pathways…just to name a few. If I had to explain this concept, I would relate it to the keys you need to start the engine of a car. Vitamin D is like a key that turns on the motor. As the function of a car is to get us to a variety of places, calcium is like the accelerator, it makes things happen and it gets our car to the destination we want. When vitamin D is activated, it stimulates the metabolism of calcium inside our cells so that a function occurs; typically the function is to make a protein. Proteins are important during times of illness. Some of the most important proteins are enzymes, antibodies, and antimicrobial peptides.
It is kind of extraordinary, that biologically our bodies know a thing or two about making vitamin D. As long as we expose our skin to sunlight which contain UVB rays, our bodies can convert inactive forms of vitamin D into active forms. The best form of exposure is 15 to 20 minutes (30 to 40 minutes if you have darker pigmentation) a day between the hours of 10 A.M. to 3 P.M. This can be difficult during the winter months when there is less sunshine and more cloudy days. Unfortunately, sitting behind a glass window is not enough to activate the vitamin D that we need to maintain a healthy immune system. Many cells within our bodies utilize vitamin D including macrophages, which are the cells that help our bodies mount an immune response. Macrophages scavenge and destroy foreign invaders or pathogens such as the pesky viruses that cause the common cold or flu.
There are 30 organs including bone, intestine, kidney, lung, muscle and skin that have nuclear receptors for vitamin D. Vitamin D nuclear receptors are a part of the so-called super-family of receptors that also includes retinoic acid (vitamin A) and hormones. Vitamin D helps to regulate cell growth, differentiation, and proliferation in many tissues. It helps premyeloid white blood cells and stem cells to differentiate into macrophages and monocytes. These immune cells help fight pathogens quickly and efficiently, making recovery faster.
Many of the immune system cells such as macrophages directly produce calcitriol or the active form of vitamin D. In macrophages, vitamin D helps with cytokine production by increasing cellular and tissue communication between other immune cells as well as regulating some inflammatory cytokines, therefore helping to ease some symptoms commonly associated with irritation during infection by the cold or flu. Importantly, vitamin D is needed by macrophages because it activates the production of antimicrobial peptides such as cathelicidin that help deal with foreign invaders.
How much vitamin D do we need? During the winter months when we are not able to make as much vitamin D due to overcast or cloudy days, we can increase our consumption. The recommended dietary allowance for people ages 19 to 50 years of age is 15 micrograms. A 3-ounce serving of pink salmon is 13.3 micrograms and 8 ounces of milk fortified with vitamin D is approximately 2.5 micrograms. A combination of these two items is 15.8 micrograms. This helps to explain why chowders are so popular in the northern states. Not only are chowders a good source of protein and dairy, but if you add vegetables like spinach and broccoli you also increase your consumption of vitamin A and vitamin C. Some mushrooms actually contain vitamin D. It can be difficult to eat when you lose your appetite due to illness, so chowders are an enticing and delicious solution. Creamed soups also provide extra calories that will help with the energy requirements needed to beat the cold and flu virus.
So when someone tells you to avoid dairy when you have a cold or flu, you can politely say, “No thank you!” Although dairy products can make mucus secretions thick, its benefits definitely outweigh the drawbacks. Besides, phlegm is just a friendly reminder to stay hydrated and to drink plenty of fluids.