Science Translational Medicine: Vitamin D Deficiency Makes Bone Age and Break

Are you getting enough sun this summer? A lack of vitamin D, the" sunshine vitamin," may speed up the aging of human bone and increase the risk of fracture, according to a new study.

The findings, published in the 11 July issue of Science Translational Medicine, suggest that a vitamin D deficiency not only reduces bone density, but also affects bone quality.

Luckily, humans can synthesize just the right amount of vitamin D in the presence of sunlight. Vitamin D is essential for absorption of calcium and its uptake into bone. Without calcium, bones cannot mineralize or rebuild and become stronger. People lacking vitamin D are at risk for many diseases, including osteoporosis.

"Vitamin D deficiency inhibits bone remodeling, which is the important biological process that continuously renews bone throughout life," said Björn Busse, researcher at the University Medical Center Hamburg-Eppendorf in Hamburg, Germany and senior author of the study.

Busse and colleagues analyzed bone samples from 30 participants, half of whom were deficient in vitamin D. They used state-of-the-art technology to characterize bone quality on the smallest of size scales, around 100 micrometers, or roughly the diameter of a human hair. The researchers also followed the development of bone cracks in real time and measured the bones’ resistance to cracking in a series of tests.

As expected, they found that vitamin D-deficient subjects had less mineralization on the surface of the bone. But underneath, bone was actually more heavily mineralized and the samples showed structural characteristics of older and more brittle bone.

The researchers noticed that these islands of mineralized bone were surrounded by a collagenous boundary, which prevented them from being properly remodeled. Cut off from a supply of osteoclasts, cells that help break down and absorb older bone tissue, these isolated sections of mineralized bone begin to age. At the same time, overall bone mineralization decreases from a lack of calcium.

The results show that domains of aged bone can develop during vitamin D deficiency and reduce bone quality, leading to heightened fracture risk. The bones become prone to breaking along tortuous cracks, rather than splitting cleanly.

"Our study shows that balancing vitamin D levels not only improves mineralization of bone, but by reintegrating old bone into the physiological process of bone remodeling, an improvement of bone quality and fracture rates can be achieved," said Busse.

Unraveling the complexity of human bone structure may provide some insight into more effective ways to prevent or treat fractures in patients with vitamin D deficiency, the researchers said.

Read the abstract, "Vitamin D deficiency induces early signs of aging in human bone, increasing the risk of fracture," by Björn Busse and colleagues.