Our bodies produce vitamin D when exposed to the sun, but does everyone, everywhere absorb enough sunlight to meet our daily vitamin D needs? Here’s what you need to know about the sunshine vitamin.
The pervading theory about how much vitamin D we can produce during sun exposure is called the latitude hypothesis. It says that our bodies can only produce vitamin D when the sun is at a significantly direct angle to where we live.
That means if you live remotely near the equator and go outside almost any time of day, you’re fine. Those nearest to the equator can produce vitamin D year-round, as long as they expose themselves to sunlight regularly.
But if you live in a place like Boston, there will simply never be enough sun to allow your body to create enough vitamin D from November through February. And in northern Canada and southern Argentina? They can’t create vitamin D for six months out of the year.
Vitamin D is so important for our health. Almost every organ in our bodies contains vitamin D receptors. Deficiency in vitamin D is associated with hormonal imbalance, osteoporosis, high blood pressure, heart disease, obesity, arthritis, and even cancer. So the fact that our bodies cannot naturally manufacture it from certain places on the Earth at certain times of year seems like a pretty big flaw in the system.
That might be because the system isn’t that simple. Here are some other factors that come into play when determining your vitamin D levels.
Maybe it’s not all about the sun after all. While food sources are generally considered inferior to sun-derived vitamin D, that may not be quite the case.
Interestingly, mushrooms are the only plant food that mimics our own skin when it comes to vitamin D absorption. That means if you expose mushrooms to UV light, even for as little as five minutes a day, their vitamin D content increases. This makes them an excellent whole food source of vitamin D for vegans or for those living through colder, darker months.
Research has shown that this mushroom-based source of vitamin D is actually as effective in the body as animal-based sources, contrary to past research.
Eggs and raw milk are other vegetarian sources of this unique vitamin/hormone, as well as an array of fish and seafoods. Food sources may be integral to supplementing vitamin D in those who are unable to produce it from the sun during spans of the year.
This may also explain why vitamin D-rich fish is such a traditional staple in colder areas of the world.
Your skin color may actually dictate how much vitamin D you are able to absorb in certain locations.
Lighter skin is more sensitive to vitamin D synthesis. As early humans expanded north and south from the equator, some scientists believe that they evolved to have a lighter skin color in order to absorb more vitamin D from the weaker sunlight.
Darker skin is slower to absorb vitamin D from sunlight, theoretically as part of the body’s powerful UV defense to the strong sun at the equator. While people with darker skin are able to absorb vitamin D easily in the tropics, they may struggle in areas of higher latitude.
Even though lighter skin is a major inconvenience when visiting tropical areas (or with any real sun exposure), it is theoretically more productive in darker, cooler climates that don’t have much sunlight.
Just as clouds can affect our absorption of important UV rays, so can pollution. Cities who struggle with real pollution issues, like Los Angeles, Salt Lake City, and Pittsburgh, may also be places where vitamin D-promoting UVB rays are harder to absorb.
TIME OF DAY
If you go outside to get some sun at nine in the morning anywhere in the northern US–even in the summer–you’re on a fool’s errand. The sun is not high enough in the sky to turn on vitamin D synthesis in our bodies.
In the height of summer, much of the northern US can only synthesize vitamin D between the hours of 10 a.m. and 4 p.m.
In order to stimulate vitamin D production, the sun needs to be at least 50 degrees or more above the horizon (maxing out at 90 degrees, or high noon). Use this handy chart to calculate what times you will be able to produce vitamin D based on your location and the day.
You’re looking for the altitude reading to be above 50. At the time of this writing, where I live in Massachusetts, I will be able to synthesize vitamin D from the sun between 10:10 a.m. until 3:30 p.m. Not a huge window at all.
Vitamin D is crucial to good health. Understanding how your lifestyle impacts your natural levels is important. And, of course, a doctor-recommended supplement is always a smart choice if you don’t work outside all day.