Objective To explore the effects of blue light on bone metabolism indexes and bone microstructure of osteoporosis model induced by retinoic acid in rats.

Methods SD rats of 9 months old were randomly divided into normal group, model group, and blue light group group 1 and group 2, with 6 rats in each group. The rats in the blue light group and the model control group were fed with retinoic acid 100 mg/kg everyday for 14 days, and the normal control group was fed with distilled water of the same volume for 14 days. After 14 days, all rats recovered to normal drinking water and food. The normal control group and the model control group were exposed to daylight lamp, and blue light group 1 and group 2 were irradiated with blue light (460 nm) mode for 14 days and 21 days respectively after retinoic acid modeling. The total exposure time of fluorescent lamp irradiation was 35 days without blue light irradiation. Blood sample was collected from the orbit of all rats 35 days later, the levels of serum calcium, phosphorus, alkaline phosphatase (ALP), β-bonded degradation products (β-CTX) and amino terminal peptide of procollagen type 1 (P1NP) were measured. After the animals were killed with CO₂ anesthesia, the bone mineral density, trabecular number, trabecular thickness, and trabecular separation of femur were measured by microCT.

Results Compared to the normal group, there were significant differences in calcium, phosphorus, ALP, β-CTX, and P1NP levels, and bone mineral density and microstructure in the model group (P < 0.01). It showed that the model was successful. Compared to the model group, the body weight, blood level of calcium, phosphorus, ALP, β-CTX, P1NP, trabecular number, trabecular thickness, trabecular separation degree in blue light group 1 were significantly changed (P < 0.05), but there was no statistical difference in bone mineral density index between the two groups. There were significant differences in body weight, bone mineral density, bone microstructure and metabolism between the blue light group 2 and the model group (P < 0.05). There were significant differences in β-CTX, trabecular number and separation between the blue light group 1 and blue light group 2 (P < 0.05).

Conclusions Blue light with 460 nm could promote the development of osteoporosis model induced by retinoic acid through early inhibition of osteogenesis and affecting calcium and phosphorus metabolism, which suggests that osteoporosis patients may need to reduce the exposure to blue light environment in their daily life.