Rheumatoid arthritis is the second most common form of joint pain after osteoarthritis. It is caused by a faulty immune system that is mistakenly attacking the body's own tissues, thinking them instead to be foreign invaders.

This chronic, inflammatory disease targets the lining of the joints, mostly in the hands and knees. It is a long-lasting, painful and frustrating form of arthritis that has no cure. More common in women than men, rheumatoid arthritis is characterized by swelling and redness and can wear down the cartilage between bones. 

Although the cause of rheumatoid arthritis is unknown, many studies have shown that vitamin D deficiency -- often caused by a lack of sunlight -- has already been associated with a variety of autoimmune diseases.

So a new group of researchers took this idea and applied it to rheumatoid arthritis. They found that women living in the northeastern United States are more likely to develop this form of joint pain. It suggests exposure to sunlight may be playing a role. The study appears online in the journal "Environmental Health Perspectives." It describes that women in states such as Vermont, New Hampshire and Maine were more likely to report being diagnosed with rheumatoid arthritis. This shows a higher risk for rheumatoid arthritis in northern latitudes, where vitamin D deficiency is more common.

While more studies are needed to address the link, everyone would do well to spend 15 minutes outside with the sun hitting their skin, without the use of sunscreen. That way, vitamin D has a chance to be absorbed more potently.