Association of Serum Prolactin Level with Impaired Glucose Regulation and Diabetes.

BACKGROUND: Increase in prolactin during pregnancy has been identified as a major stimulus for ß cells. These effects have been demonstrated in both in-vitro and in-vivo non-pregnant animal models. Recently, bromocriptine has also been approved for the therapy of type 2 diabetes, regardless of the baseline prolactin level, with its mechanism of action poorly understood. Hence, this study was planned to assess whether prolactin levels within normal range associates with prediabetes and diabetes. METHODS: A total of 300 participants, 180 males and 120 females, with equal number of subjects in the prediabetes, diabetes and normal group were analyzed. The participants were categorized into sex-specific quartiles of serum prolactin, with the first quartile representing subjects with the lowest prolactin levels and the fourth quartile having the highest levels. In addition, multinomial logit analyses were performed to evaluate the odds ratio and 95% confidence interval of having prediabetes & diabetes for each quartile. RESULTS: Prolactin levels in the normal group were 10.99 ± 3.65 ng/ml for the males and 12.25 ± 3.67 ng/ml for the post-menopausal females. The prolactin levels for the males in prediabetes group were 9.46 ± 3.43 ng/ml and for diabetes group were 8.98 ± 3.43 ng/ml (p value = 0.005). In females, the prolactin levels were 10.20 ± 3.99 ng/ml for the prediabetes group and 9.60 ± 3.85 ng/ml for the diabetes group (p value = 0.007). The mean fasting plasma glucose for the four male quartiles in their numerical order were 135 mg/dl, 128 mg/dl, 120 mg/dl and 110 mg/dl (p value = 0.04) and the mean HbA1c in the same order for the quartiles were 7%, 6.4%, 6.1% and 5.9% (p value = 0.01). Similarly, the mean fasting plasma glucose for the four female quartiles in their numerical order were 138 mg/dl, 131 mg/dl, 124 mg/dl and 107 mg/dl (p value = 0.03) and the mean HbA1c in the same order for the quartiles were 7.2%, 6.7%, 6.3% and 5.8% (p value = 0.01). The age adjusted odds ratio for 2nd, 3rd and 4th quartiles as compared to the 1st quartile for prediabetes in men were 0.82, 0.72 and 0.61 and for diabetes were 0.84, 0.65 and 0.55, respectively. Risk for diabetes in females ranged from 0.04 to 0.72 for the 3rd quartile and 0.03 to 0.56 for the 4th quartile as compared to 1st quartile. The risk for prediabetes in females ranged from 0.06 to 0.95 for 3rd quartile and 0.04 to 0.74 for the 4th quartile as compared to 1st quartile. CONCLUSIONS: Mean prolactin levels in both males and females were lower in prediabetics and lowest in diabetics. Prolactin, on quartile based analysis, associated with better HbA1c and fasting plasma glucose. Decreasing relative risk trends for both prediabetes and diabetes were found with increasing serum prolactin concentrations. No association was found with obesity and dyslipidemia.