We’ve been interested in the role vitamin D plays in our overall health for a while—particularly as it emerges that so many of us are quite deficient, particularly in the age of sitting inside all day and sunscreen. “Vitamin D” is sort of a misnomer because it doesn’t really behave like a vitamin; rather it functions more like a hormone. The form you typically consume (in food or supplements, or indirectly via the sun) is vitamin D3, but your body converts this into a steroid hormone, called calcitriol. Once vitamin D is turned into this active form, it travels throughout the body and plays a part in a number of diverse (and vital) functions: It builds bones and muscles; it also has anti-inflammatory effects, and helps to make enzymes and proteins that prevent diseases; it affects aging. High levels of vitamin D have been linked to stronger immune systems, while low levels are associated with cardiovascular disease, diabetes, and cancer. The full extent of vitamin’s D impact has yet to be fully understood—nearly every cell and tissue in our body has vitamin D receptors (proteins that bind to vitamin D); and in its active form, vitamin D can interact with the vast majority of the body’s cells. Below, vitamin D expert, Rhonda Patrick, Ph.D., shares the latest research on vitamin D (including some of her own)—which touches on aging, mood, autoimmunity, and autism (to name a few)—and spells out how to be sure you’re getting enough.
A Q&A with Rhonda Patrick, Ph.D
How many people globally are thought to be vitamin D deficient, and how does that compare to the U.S.?
First, we need to define “vitamin D deficiency.” The U.S. Endocrine Society, which uses a medical model that considers the broader set of vitamin D3 functions instead of just those related to bone, recommends that serum vitamin D levels above 30 ng/ml are adequate, levels between 29 ng/ml and 20 ng/ml are inadequate, and below 20 ng/ml are deficient. If we are to use this definition of adequate, much of the world falls in the category of either inadequate or deficient. According to meta-analyses of several studies that have assessed serum vitamin D3 levels worldwide, the global average vitamin D3 level is actually 20 ng/ml, which is pretty close to full-on deficient…and that’s the average. In the United States, approximately 70% of the population has vitamin D levels below 30 ng/ml.
Is our modern lifestyle (more time at the computer, less outside) and increased sunscreen use the major cause of this widespread deficiency, or do other factors play into the epidemic?
Yes, it is generally thought that the main reasons why vitamin D3 levels have decreased over the last few decades is due to more sunscreen use and spending more time indoors on computers. Since UVB radiation from sunlight is required to produce vitamin D in the skin, anything that blocks UVB rays such as sunscreen will also prevent your skin from making vitamin D3.
Another possible contributing factor to low vitamin D3 is the increased obesity epidemic. Vitamin D3 is a fat-soluble vitamin, which means it is stored in our fat. A higher body fat percentage can decrease the bioavailability of vitamin D3 by as much as 50% by soaking up the vitamin D and preventing it from making its way to our other tissues. This means that overweight and obese individuals may have less vitamin D that is available to be used by the body.
Other factors that regulate the ability of the skin to make vitamin D3 include age (a seventy-year-old makes about four times less vitamin D3 from the sun than a twenty-year old); melanin, which acts as a natural sunscreen; and latitude, which dictates whether UVB rays can reach the atmosphere.
Beyond skin coloration and latitude, what else determines how much vitamin D a particular individual needs? Are there genetic differences?
Genetics also play an important role when it comes to vitamin D. Gene polymorphisms, normal variations in the sequence of DNA of a gene that can alter its function, exist in several different genes involved in the vitamin D pathway. One gene that is subject to these sort of variations that can either affect how good we are at converting the precursors of what we normally call “vitamin D,” 25-hydroxyvitamin D, is known as CYP2R1. If we have a polymorphism that makes this gene less efficient at doing its’ job, then we’ll see less 25-hydroxyvitamin D being converted in the kidneys, and this will show up on the blood test we can get at our doctor’s office. In the future, we may see this giving us valuable insights since it may mean that certain individuals would have to take more vitamin D in order to achieve “sufficiency.”
What role does vitamin D play in aging?
Vitamin D3 is actually much more than a vitamin; it gets converted into a steroid hormone that has been shown to affect the activity (expression) of almost 1,000 different genes in the body, which is about 4.6% of the human protein-encoding genome! Let that sink in for a moment. I wouldn’t want 5% of the parts in my car engine to be working inappropriately if I wanted the car to have longevity!
But…returning to your question: Vitamin D does seem to affect the way we age. Mice that have been genetically engineered to not be able to respond to vitamin D (a vitamin D receptor “knockout”) manifest dramatic signs of aging in all the organs on a cellular level. You do not want to be these mice. There are multiple mechanisms by which vitamin D regulates the aging process, including telomeres. Every cell in your body contains DNA, which is present in your chromosomes, and the integrity of your DNA is crucial for your cells to function properly. Telomeres, which are caps at the end of chromosomes, help maintain that integrity. They protect our DNA from damage and deterioration. The length of our telomeres has been shown to correlate pretty well with our biological age. In this capacity, they serve as a marker for aging. If you have short telomeres, you’re biologically old. If you have long telomeres, you’re biologically younger. As in all things, there’s more nuance to it than that, but for our purposes, it’s useful to realize that we can be chronologically older, but have a biological age that is in line with those younger than us.