Fluoride and Alkaline Phosphatase

Since serum alkaline phosphatase increases in fluoride therapy for osteoporosis, it is generally accepted that fluoride stimulates bone formation. However, histochemical studies have shown that alkaline phosphatase is also increased in resorbing osteocytes. Fluoride is toxic to metabolically active bone cells, alkaline phosphatase is released, and serum alkaline phosphatase increases. We propose that the increased serum alkaline phosphatase following fluoride therapy may reflect a toxicity of fluoride for both osteoblasts (bone forming cells) and resorbing osteocytes. When cells are injured their first response is to initiate repair processes and if this repair fails the cell dies. An increase of serum alkaline phosphatase and increased bone mass following fluoride therapy represent a failed repair response involving an initial increase in both bone formation and resorption. This repair response to cell injury results in pathological bone formation. Furthermore, as the repair process fails there is a toxic death of resorbing osteocytes and a decrease in bone resorption. Osteoclasia of fluorotic bone may result in secondary toxic effects of fluoride on osteoclasts, and contribute to decreased bone resorption. The increased amount of trabecular bone in fluoride therapy is claimed to be the morphologic expression for fluoride as a stimulus for bone formation. We propose that the increased amount of trabecular bone results from pathological bone formation by injured osteoblasts and decreased bone resorption by resorbing osteocytes and osteoclasts. Both resorptive processes are required for the remodeling of trabecular bone into compact bone. Fluoride has only negative effects on bone cell metabolism. Fluoride should be avoided, especially in osteoporosis.