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Introduction: The prevalence of type 2 diabetes mellitus (T2DM) is increasing worldwide. Strategies to decrease this risk should be strongly encouraged. Lactation has been associated, for the mother, with reduction in future T2DM risk in several studies. The mechanisms behind this phenomenon, however, are poorly understood. The aims of this study were, first, to compare blood glucose levels and markers of insulin resistance (MIR) in early postpartum women with overweight/obesity according to their breastfeeding status and, second, to evaluate whether prolactin (PRL) levels could mediate improvements in these parameters. Methods: The prospective study followed 95 women older than 18 years from early pregnancy for up to 60 to 180 days postpartum. All participants had a BMI > 25 kg/m2 and a singleton pregnancy. At each visit, questionnaires and clinical and biochemical evaluations were performed. Participants were divided into two groups according to the breastfeeding status as "yes" for exclusive or predominant breastfeeding, and "no" for not breastfeeding. Results: Breastfeeding women (n = 44) had significantly higher PRL levels [47.8 (29.6-88.2) vs. 20.0 (12.0-33.8), p< 0.001]. They also had significantly lower fasting blood glucose levels [89.0 (8.0) vs. 93.9 (12.6) mg/dl, p = 0.04], triglycerides (TG) [92.2 (37.9) vs. 122.4 (64.4) mg/dl, p = 0.01], TG/HDL ratio [1.8 (0.8) vs. 2.4 (1.6) mg/dl, p = 0.02], TyG index [8.24 (0.4) vs. 8.52 (0.53), p = 0.005], fasting serum insulin [8.9 (6.3-11.6) vs. 11.4 (7.7-17.0), p = 0.048], and HOMA-IR [2.0 (1.3-2.7) vs. 2.6 (1.6-3.9), p = 0.025] in the postpartum period compared to the non-breastfeeding group. Groups were homogeneous in relation to prevalence of GDM, pre-gestational BMI, as well as daily caloric intake, physical activity, and weight loss at postpartum. Linear regression analysis with adjustments for confounders showed a statistically significant association of breastfeeding with fasting blood glucose [-6.37 (-10.91 to -1.83), p = 0.006], HOMA-IR [-0.27 (-0.51 to -0.04), p = 0.024], TyG index [-0.04 (-0.06 to -0.02), p = 0.001], and TG/HDL ratio [-0.25 (-0.48 to -0.01), p = 0.038]. Mediation analysis showed that PRL did not mediate these effects. Sensitivity analyses considering different cutoffs for PRL levels also did not show modification effect in the mediation analyses. Conclusion: Breastfeeding was associated with improvement in glucose metabolism and MIR 60 to 180 days after birth in overweight and obese women, even when adjusted for confounders. PRL levels were not found to mediate the association between breastfeeding and improvement in MIR.

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The role of prolactin (PRL) favoring metabolic homeostasis is supported by multiple preclinical and clinical studies. PRL levels are key to explaining the direction of its actions. In contrast with the negative outcomes associated with very high (>100 µg/L) and very low (<7 µg/L) PRL levels, moderately high PRL levels, both within but also above the classically considered physiological range are beneficial for metabolism and have been defined as HomeoFIT-PRL. In animal models, HomeoFIT-PRL levels counteract insulin resistance, glucose intolerance, adipose tissue hypertrophy and fatty liver; and in humans associate with reduced prevalence of insulin resistance, fatty liver, glucose intolerance, metabolic syndrome, reduced adipocyte hypertrophy, and protection from type 2 diabetes development. The beneficial actions of PRL can be explained by its positive effects on main metabolic organs including the pancreas, liver, adipose tissue, and hypothalamus. Here, we briefly review work supporting PRL as a promoter of metabolic homeostasis in rodents and humans, the PRL levels associated with metabolic protection, and the proposed mechanisms involved. Finally, we discuss the possibility of using drugs elevating PRL for the treatment of metabolic diseases.

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Estudio no experimental, prospectivo, comparativo y longitudinal, realizado con el objetivo de comparar los niveles de prolactina en 15 madres (Grupo estudio) con más de dos semanas de haber suspendido la lactancia materna y entrenadas para relactar según método recomendado por Organización Mundial de la Salud: Estimulación del pezón y del pecho, Técnica de chorrear y gotear y Extracción mecánica y manual y en 25 madres (grupo control) que lactaban en forma exclusiva, cuyos hijos menores de seis meses, fueron hospitalizados por diversas patologías, en la División Pediátrica del Servicio Autónomo Hospital Universitario de Maracaibo, desde noviembre 2010 a octubre 2011. Las madres tuvieron entre 15 y 25 años de edad en ambos grupos (p=0,58); la causa principal del abandono de la lactancia fue escasa producción láctea (46,67%).El tiempo de aparición de la secreción láctea fue de 6+1,60 días.Los niveles de prolactina de madres del grupo estudio en las primeras 24 horas del ingreso del lactante fue 35,58+18,04 ng/ml y en el grupo control 129,83+35,01 ng/ml, estadísticamente significativo (p=0,01). Iniciada la secreción láctea fue de 121,20+16,90 ng/ml, estadísticamente significativo (p=0,01) comparado con el valor inicial del grupo estudio, pero al comparar con el grupo control fue estadísticamente no significativo (p=0,13).Se concluye que en este grupo de madres que abandonaron la lactancia, una vez iniciada la relactación presentaron un aumento significativo de los niveles de prolactina, similares a los niveles en madres lactando en forma exclusiva.

Not experimental, prospective, comparative, and longitudinal study conducted in order to compare the levels of prolactin in 15 mothers (study group) with more than two weeks of having suspended the breastfeeding, and trained to relactate according to the method recommended by World Health Organization: nipple and breast stimulation, technique of dripping and drip and mechanical and manual removal, and 25mothers (control group) that breastfeeding exclusively, whose children less than six months, were hospitalized with various diseases, in the Division of Pediatric of University Hospital in Maracaibo, from November 2010 to October 2011. The mothers had between 15 and 25 years of age in both groups (p =0.58), the main cause of the abandonment of breastfeeding was insufficient milk production (46.67%). The time of occurrence of milk secretion was 6+1.60 days. Prolactin levels in the study group mothers in the first 24 hours of admission was 35.58+18.04 ng/ml, and in the control group 129.83+ 35.01 ng/ml, statistically significant (p=0.01). Initiated the milk secretion was 121.20+16.90 ng/ml, statistically significant (p =0.01 compared to base line study group, but when was compared to the control group was not statistically significant (p =0.13). It concludes that in this group of mothers who left nursing, once started relactation had significantly higher prolactin levels, similar to the levels in mothers exclusively breastfeeding.

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