Welcome to Straight Talk on Health. I’m your host Dr. Chet Zelasko. Straight Talk on Health is a joint production with WGVU in Grand Rapids MI. I examine the practical application of health information. Nutrition. Exercise. Diet. Supplementation. I look at the science behind them, and let you know whether it’s something to consider or not. You can check out other things that I do on my website Drchet.com and sign up for my free emails.
As I record this podcast, it’s winter. It got me to wondering, after a serum vitamin D test that was much lower than I expected, how much vitamin D am I making at this time of year? Time to get back to basics.
I set out to find what factors impact Vitamin D levels in human beings. What I found was really informative. I knew the biochemistry of vitamin D and how complex the manufacturer of vitamin D in the skin really is. In addition to the skin, there are a variety of factors that can impact the manufacturer of vitamin D in the body. I thought it would be very informative to share what I found. Sometimes, what seems to make sense to us and what we think is true, is not necessarily the way it really is. So let's take a look add the factors that impact Vitamin D levels made by the skin in the body.
The first area of focus is that there is a rate limiting enzyme that controls the conversion and production of vitamin D two active levels. Vitamin D is dependent on Vitamin D hydroxylase. The vitamin D hydroxylase acts as a governor of sort. If you’ve ever driven a large truck or tractor-trailer, you’d know what a governor is—you can’t exceed the RPMs faster than it is set. Same thing here. No matter how much sun you're exposed to, you will only make so much vitamin D. It simply stops the process when it senses that enough vitamin D has been made. That’s why you never over produce vitamin D to where it might get to toxic levels by your bodies action alone. The body stops that process.
The critical factor in production of vitamin D by the skin is the amount of UVB radiation. This radiation takes up a very specific part of the electromagnetic spectrum. That spectrum lies between 280 nanometers to 320 nanometers. If you want to get particular about it, the optimal wavelength for vitamin D is 297 nanometers which is midway between the optimal range of 295 and 300 nanometers. With that being so specific, anything that can impact that wavelength can impact our ability to make vitamin D. As it turns out, there are plenty of them.
It surprised me to find out that ozone in the stratosphere or at ground levels can impact the wavelength of UVB radiation. This is not about global warming or weather change. There is a natural variability of the ozone layer throughout the year in different parts of the world. Based on several studies, a 12 1/2% decrease in the ozone level in any given area can increase the amount of UVB radiation by 15%. When you consider it , that's pretty amazing but it also means that opens up the possibility of excess skin damage if one spends too much time in the sun. That's a topic for another day.
It also makes sense that pollution could have an impact on the radiation wavelength of UVB. Whether it is water vapor, pollutants of coal burning plants, aerosols, all of those things can have an impact on the UV radiation available. Just for a second, consider water vapor. The amount of water vapor in the air on a cloudy day can have a significant impact on UVB radiation by diffusion the sun's rays as it comes down. You can get a sunburn on a cloudy day and as a longtime runner, I can assure you that that's true. But you wouldn't be making very much vitamin D because the UVB radiation may not be getting through.
Let's get to what I feel is probably the most important factor to the production of vitamin D from the environment. That's something called the solar zenith angle. The solar zenith angle is the angle between a vertical and a line from the observer to the sun. As an example, when the sun is directly overhead during the summer, the solar zenith angle is at optimal for the production of vitamin D by the skin. But as the time of year changes, so does the solar zenith angle. That means that the sun's rays would have to go through more of the atmosphere which can interfere with its ability to get through. When it's summer time and the sun is directly above, that's the shortest distance but as we continue the path around the sun and the earth rotates, that angle changes. In the middle of winter, even if the sun were directly above your head, the solar zenith angle would be such that you might not produce any vitamin D at all.
The solar zenith angle is dependent on the time of day, the time of year, and the latitude of the individual at any specific point in time. That means that the vitamin D levels between people who live on 45th parallel, such as northern cities in Oregon, Minnesota, Michigan, and Maine, and those that live along the 35th parallel, such as cities in AZ, TN, and NC could be lower as we move from the latitude further south to north such as Memphis north to Minneapolis. The solar zenith angle will be different but how about the vitamin D levels. Does that guarantee a person will make more vitamin D the further south they live? Maybe but there is no guarantee if they spend more time indoors
When we're talking about the flu or other type of viral infections, the timing of when those illnesses occur turns out to be critical. One of the other facts that I learned is that if we did not get vitamin D from our diet, from exposure to the sun, or from supplements, we would have a roughly 2 month supply stored in our fat. Those of us in MI and further north could be coming out of the winter season in February. We could be relying on our stored vitamin D. That’s the time of year when the risk for viral infections is high. We could almost have no reserves of vitamin D to help our immune system.
Those are all the environmental factors that can impact our skin's production of vitamin D. What are some of the other factors? Clothing. Our clothing can limit the amount of UVB radiation that gets through clothes. When you consider that we typically don't walk around nude in this society, what we wear may be able to have an impact on how much vitamin D we can produce. It turns out that natural fibers , especially cotton, can have a greater impact on how much Vitamin D we produce. Why? It turns out that they allow more UVB radiation through. Synthetic fibers have a tendency to allow less UV radiation through.
Something else that has a great impact on the ability of the skin to make vitamin D is actually the temperature of that skin. As you might expect, the best production comes at 37 degrees centigrade which corresponds to 98.6 Fahrenheit. That's the optimal temperature but we know that skin temperature doesn't necessarily always match internal temperature. A variety of factors such as the ambient temperature, air flow, air pressure, and humidity can all impact skin temperature. Depending on where you live, you may or may not understand wind chill. Especially in the fall, when you start to get the impact of the solar zenith angle, adding factors that reduce skin temperature can also reduce the amount of vitamin D that you will be able to make.
Are we done yet? When you consider all of the things that have to be right to make vitamin D, it's a wonder we make any at all. But there is one more factor in all of this. Being overweight or obese can also impact your ability to store the vitamin D that your body has worked so hard to make. In some studies where they have used UVB irradiation under controlled conditions, people that were obese made up to 57% less vitamin D then controls who were normal weight. And it doesn't only impact Vitamin D production. In the same study, after taking a single dose of 50,000 international units of vitamin D, the rate of actual absorption was inversely proportional to the degree of obesity. Simply put, the more overweight an individual, the less vitamin D that they get both from skin production and from the supplements that they make.
So there it is. Everything that can impact the production of vitamin D in your body that we know of today. There is no doubt specific genes for the manufacture of vitamin D or it’s receptor on cells that have mutations can impact vitamin D levels but this is the state today. What we do with the information is up to us. I think getting a reasonable amount of sunshine during the right time of the year and building a safety net with complementary nutrition based on our vitamin D levels is the right way to go for helping get our immune system as strong as it can be. That’s it for this episode. Until next time, this is Dr. Chet Zelasko saying health is a choice. Choose wisely today and every day.
