Osteoporosis, a condition that weakens bones, causes over 500,000 fractures per year in the UK. This number is likely to increase as the average age of our population goes up. Our bone strength is determined by many factors, including genetics, load-bearing exercise, and blood flow to the bones. Scientists have recently identified a type of capillary in bone, called type H. When blood flows through these fine vessels it switches on a messenger molecule called Notch, which triggers bone growth. Type H capillaries are shown in red in this cross-section of mouse bone. Bone loss due to ageing could be because the reduced blood flow in older individuals leads to less Notch. Treating older mice with bisphosphonates, the current treatment for osteoporosis, switched Notch back on and increased blood flow to the bones. This all points to blood flow being more closely linked to bone growth than previously thought.
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