The list of reasons for why headaches occur can seem almost endless: stress, anxiety, eye strain, colds, fevers, arguments with people that--however difficult this is to imagine--don't love Monty Python, certain smells, harsh lighting, allergies...the list goes on and on.

Now there's another item you can add to that list: vitamin D deficiency.

Fortunately, that problem is easy to solve.

First the science. According to a new study from the University of Eastern Finland, vitamin D deficiency can increase the risk of chronic headaches. ("Chronic" was defined as experiencing at least one headache a week.)

In fact, participants with the lowest levels of serum vitamin D were twice as likely to experience chronic headaches than those with the highest levels of serum vitamin D. (Basically, "serum" refers to the vitamin D found in your blood.) Chronic headaches were also more frequently reported by all participants examined during the winter months; because we absorb vitamin D from sunlight, average levels tend to be higher in the summer.

"There are vitamin D receptors in the sensory neurons in the brain involved in pain," says Jyrki Virtanen, the lead researcher of the study. "So being deficient may directly affect these neurons."

Reason enough to take a vitamin D supplement, especially if you're prone to headaches...but wait. There's more!

Other symptoms of vitamin D deficiency include muscle weakness, increased blood pressure, depression, heart disease...and specifically for men, prostate cancer and erectile dysfunction.

That's a delightful little list, but there's one more reason to make sure you get enough vitamin D. It's possibly the best reason of all, especially if you're like me and old enough to have started worrying about the effect of age on your memory.

Older adults with low vitamin D levels may lose their memories and thinking abilities faster than those with normal vitamin D levels, according to a broad range of research. (Here's just one example.)

Among people with cognitive impairment, 70 to 90 percent don't get enough vitamin D.

Yep: 70 to 90 percent of the people studied who had cognitive impairment were deficient in vitamin D.

Low vitamin D levels were associated with greater difficulty remembering general information, finding your way in your environment, and managing your overall thinking process.

Unfortunately, getting enough vitamin D isn't easy. Fatty fish, dairy products, eggs, and some cereals are all good sources, but relatively few people get sufficient vitamin D from their diet.

Fortunately, there's an easy fix: Take a vitamin D supplement.

You don't need a lot. Since it is possible to get too much vitamin D--the Institute of Medicine recommends 4000 IU per day as an upper limit--taking a supplement with 2000 IU per day is likely to be plenty, especially since the recommended daily amount is 600 IU. (As always, talk to your doctor for guidance specific to your individual needs.)

Most multivitamins include vitamin D, but the IUs tend to be lower than those found in a stand-alone supplement. (For example, this multivitamin has 500 IU of vitamin D.)

If you get frequent headaches, add a vitamin D supplement to your daily regimen. And even if you don't get frequent headaches, do it anyway.

With apologies to Descartes: You think, therefore you are. So do your best to make sure it stays that way.