Vitamin D is sometimes called the "sunshine vitamin" because your body produces it in the presence of sunlight.
A lack of vitamin D leads to early signs of aging in human bones and increases the risk of fracture, a new study suggests.
The study was published in the journal Science Translational Medicine on Wednesday, July 10.
Vitamin D, which your body produces naturally when ultraviolet rays in sunshine strike the skin, is essential for the absorption of calcium. It's what enables our bones to harden, or mineralize, as well as rebuild and become stronger.
In northern parts of the world, insufficient sunlight is one of the main causes of vitamin D-deficiency, says lead author Dr. Björn Busse of the University Medical Center in Hamburg. A lack of vitamin D leads to diseases like osteoporosis, when the bones become weak and can break easily, or osteomalacia, when the bone becomes soft because they do not mineralize properly. The softening of the bones in children is called rickets.
For this study researchers studied bone samples from 30 healthy people. Half of the samples were determined to be deficient in vitamin D. The reason for the deficiency is unknown but Busse suspects that low exposure to sunlight was a major reason as all participants were from the area around Hamburg in Northern Germany.
As expected, the bones of vitamin-D deficient subjects were different than normal subjects. People lacking in vitamin D had a thicker layer of unmineralized bone on the outside of their bones. Surprisingly, researchers found denser mineralized bone than normal underneath this layer. The heavily mineralized bone had "the structural characteristics of older and more brittle bone," the authors write.
This happens because the thick mineralized bone slows the movement of osteoclasts, the cells responsible for new bone formation, through the bone. These sections of mineralized bone continue to age and mineralize, while overall bone mineralization declines because of a lack of calcium.
"Vitamin-D has been known to be important for bone health; however, the increase in fracture risk was assumed to be completely due to less mineralization," said Busse. "Here, we show that domains of aged bone also exist and influence the fracture risk."
The Institute of Medicine recommends that men and women between the ages of 14 and 50 get 600 IU of vitamin D per day. Since very few natural foods contain vitamin D, the best way to hit the target amount is by exposing your skin to bare sunlight for 10 or 15 minutes each day (you don't need to get a tan and should be careful not to burn). People who live in countries with low sunlight exposure can eat foods that are fortified with vitamin D, including milk, breakfast cereals, and orange juice, or take vitamin D supplements.
Understanding the negative effects of of not getting enough vitamin D "may provide some insight into more effective ways to prevent or treat fractures in patients with vitamin D deficiency," according to the study.
A side-by-side comparison of normal bone samples (left) and vitamin-D deficient ones is seen in the graphic below. In patients lacking vitamin D there are cracks between the excess of non-mineralized bone on the surface of the bone (osteons) and highly-mineralized bone.
Science Translational Medicine/AAAS
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