Context: Osteocalcin or Bone Gla Protein (BGP) is a bone specific protein. It is the major and most thoroughly characterised noncollagenous protein in mature human bone. Osteocalcin is now considered as an important marker for bone turnover. Vitamin D status plays an important role in mineralisation of the skeleton at all ages.

Aims: The present study was designed to evaluate: the prevalence of hypovitaminosis D in post-menopausal females, significance of serum osteocalcin in evaluation of osteoporosis, and to determine the effect of risedronate therapy on serum osteocalcin in post-menopausal females with osteoporosis.

Materials and methods: One hundred and forty-eight post-menopausal women between 40 to 80 years attending the hospital OPD were studied. To be eligible for the study they had to have been post-menopausal for at least one year and had decreased bone mineral density (lumbar spine or right or left femoral neck or both T-score-1.0 or less). The diagnosis of osteoporosis was made based on T-scores (BMD) at the lumbar spine (L1 to L4) and femoral neck by DEXA (GE Lunar Densitometer). Patients with chronic conditions affecting skeletal health and patients on drugs affecting the skeleton were excluded from the study. Serum 25 (OH) vitamin D was estimated using LIAISON 25 OH Vitamin-D chemiluminescent immunoassay. Osteocalcin level in the serum was estimated by LIAISON Osteocalcin assay. Patients with osteoporosis were treated with risedronate 35 mg/week and were reassessed after 1 year.

Results: Out of 148 post-menopausal females, 101 subjects had vitamin D deficiency (≤ 20 ng/ml) and 30 subjects had vitamin D insufficiency (21-29 ng/ml). Thus, prevalence of hypovitaminosis D in post-menopausal females was 88.51%. Serum osteocalcin was found to be significantly higher in post-menopausal women with osteoporosis as compared to post-menopausal women without osteoporosis (p< 0.05). On correlation analysis, inverse relationship was found between BMD and serum osteocalcin levels (r2=-0.770, p< 0.05). There was a significant reduction in serum osteocalcin after 1-year treatment with risedronate (p< 0.05).

Conclusion: Serum osteocalcin is a promising marker of bone turnover in post-menopausal women with osteoporosis, as it was found to be elevated in osteoporosis; also, its level reduced after treatment with risedronate. Therefore, osteocalcin provides a dynamic measure of bone remodelling and it can be potentially useful in diagnosis and monitoring of response to therapy in patients of osteoporosis. We also concluded that hypovitaminosis D is very common in our clinical setup, thus underlining the importance of adequate calcium and vitamin D supplementation before starting bisphosphonates or any other specific treatment for osteoporosis.