About 90 percent of the world’s population live in the Northern Hemisphere, where sunlight is simply not very accessible year-round. That means that, for nine out of every ten people on the planet, it is very easy to become Vitamin D deficient. As you know, Vitamin D is a hormone delivered to us by the sun. If you’re getting lots of sunlight, it’s probably safe to assume that you’re not deficient in Vitamin D. If you’re life most people, however, you’re only getting sun a few months out of the year, and then the opposite assumption can be made: you probably don’t have as much Vitamin D in your body as you need. Indeed, one study by the Journal of the American College of Nutrition found that 74% of Americans were not taking in as much Vitamin D as they ought to be.

Mostly, Vitamin D plays a crucial role in skeletal growth and health, as well as calcium stability. Low Vitamin D is widely understood to be a risk factor for bone disorders like osteoporosis. But did you know that it’s also linked to an increased risk of various cancers, as well as depression, hypertension, cardiovascular disease and autoimmune disorders like fibromyalgia?

That’s a long list of serious health complications that may be caused in part by low levels of a hormone that most of us tend to have a cavalier attitude towards.

Here’s an excerpt from the abstract of a study that researched the connection between low Vitamin D and cancer:

“Because most physicians do not appreciate the role of vitamin D deficiency in predisposing the development of cancer, we have written this important report as a wake-up call to physicians and other healthcare workers in documenting the relationship of vitamin D deficiency and cancer. Epidemiological data show an inverse relationship between vitamin D levels and breast cancer incidence. In addition, there is a well-documented association between vitamin D intake and the risk of breast cancer. Low vitamin D intake has also been indicated in colorectal carcinogenesis. A vitamin D deficiency has also been documented in patients with prostate cancer, ovarian cancer, as well as multiple myeloma.”

Links between Vitamin D and high blood pressure are still being researched, but a correlation has been observed:

“Because of the opposing consequences of different reviews on the role of Vitamin D in preventing hypertension development or its treatment, it appears that Vitamin D levels in the body modulate the blood pressure indirectly. More studies should be conducted after eliminating the compounding factors in order to prove the association. We suggest that physicians should keep a check on the Vitamin D levels of their patients in order to curb the ever-increasing incidence of hypertension.”

Given high blood pressure’s role in causing cardiovascular disease, it’s unsurprising to learn that Vitamin D is also linked to these conditions. From one study:

“Cross-sectional studies have reported that vitamin D deficiency is associated with increased risk of CVD [cardiovascular disease], including hypertension, heart failure, and ischemic heart disease. Initial prospective studies have also demonstrated that vitamin D deficiency increases the risk of developing incident hypertension or sudden cardiac death in individuals with preexisting CVD.”

So, next time you visit your doctor, request that he or she test your Vitamin D levels. If they’re low—and there’s a good chance they are—work with your doctor to develop of a responsible, long-term regimen to bring your level of this critical hormone up into the optimal range. You will thank yourself later.