Serum Sclerostin Levels Vary With Season

Context: To establish the clinical utility of serum sclerostin levels, it is important to know whether there is seasonal variation in the measurements. Objective: This study was done to determine whether serum sclerostin levels vary by season in healthy older men and women. Methods: Serum sclerostin levels were measured in archived serum of 314 healthy men and women aged 65 years and older and examined for seasonal variation. Several factors known to vary by season and previously reported to be associated with serum sclerostin levels, including serum osteocalcin, physical activity, and serum PTH levels, were also measured in these subjects. Sex did not modify the association of season with sclerostin, so the men and women were analyzed together. Results: Serum sclerostin levels varied significantly by season (P < .001, after adjustment for sex). Sclerostin levels in the wintertime were 20% higher than the all-year mean, the levels gradually declined through the spring and summer, and by the fall, they were 20% below the all-year mean. Adjustment for serum osteocalcin, physical activity, and serum PTH did not alter the seasonal means. Seasonal differences in serum osteocalcin, physical activity, and serum PTH were not statistically significant. Conclusions: This study documents marked seasonal variation in serum sclerostin levels. It is important to recognize this source of biological variability when considering the potential clinical utility of sclerostin measurements.