Metformin in Fathers
Turning to fathers, a much larger cohort study by Harvard T.H. Chan investigators looked at the effect of paternal metformin use and also found it to be safe.
The Harvard investigators analyzed diabetic men in 383,851 live births from 1999 to 2020 in an Israeli health fund cohort, excluding those with diabetic spouses. Across different T2D medication groups, paternal age ranged from about 35 to about 43 years. The data revealed that paternal use of metformin monotherapy in the preconception sperm production period was, after adjustment of crude numbers, not associated with major congenital malformations (MCMs) in newborns.
“While metformin has an overall good safety profile, it can lower androgen levels, and there had been some concerns that its use in fathers could alter the sperm, causing adverse effects to the fetus,” lead author and neuroepidemiologist Ran S. Rotem, MD, ScD, of the Harvard School of Public Health, Boston, Massachusetts, said in interview. “Given the increasing prevalence of diabetes in young individuals, more fathers are conceiving a child while using the medication, which could lead to a substantial population effect even if the individual risk is low. But our study suggests that the medication is safe to use by fathers before conception.”
Dr. Ran S. Rotem
The prevalence of MCMs in the cohort was 4.7% in children of fathers unexposed to diabetes medications (n = 381,041), compared with 6.2% in children of fathers exposed during preconception spermatogenesis to metformin (n = 1730).
By these crude numbers, children with preconception paternal metformin exposure had a nearly 30% increased odds of MCMs. But whereas the crude odds ratio (OR) for MCMs with paternal metformin exposure in all formulations was 1.28 (95% CI, 1.01-1.64), the adjusted OR was 1.00 (95% CI, 0.76 -1.31). Within specific regimens, the adjusted OR was 0.86 (95% CI, 0.60-1.23) for metformin in monotherapy and 1.36 (95% CI, 1.00-1.85) for metformin in polytherapy.
At the outset, Dr. Rotem’s group hypothesized that any crude associations between metformin in polytherapy and birth defects could potentially be explained by poorer underlying parental cardiometabolic risk profiles in those taking multiple diabetes medications. Compared with that of unexposed fathers, the prevalence of cardiometabolic morbidity was indeed substantially higher among both fathers who used metformin during spermatogenesis and their spouses.
In addition, these fathers were more likely to be older, to be smokers, and to have fertility problems. Similarly, mothers were more likely to have cardiovascular comorbidity and to have had fertility problems when the father used metformin.
Moreover, children born to men who used diabetes medications before conception were much more likely to have mothers who also had diabetes and other metabolic conditions, Dr. Rotem noted. “This makes sense since we know that many of these conditions are affected by diet and lifestyle factors that are probably shared across individuals living in the same household.”
Recent research has shown that paternal health and behavior before conception can affect offspring development and long-term health. Characteristics including obesity, diabetes, and metabolic syndrome are seen to affect offspring via complex indirect and direct mechanisms, both genetic and nongenetic.
Doing little to dispel safety concerns, a recent Danish national study reported a link between preconception paternal metformin and major birth defects, particularly genital birth defects in boys. That study, however, lacked data on medication adherence and glycemic control.
“These are well-conducted studies, but it would be useful to see them replicated in different populations, as the sample sizes eligible for analysis are relatively small and some of the confidence intervals are wide,” said Robert W. Platt, PhD, a professor in the departments of Pediatrics and of Epidemiology, Biostatistics, and Occupational Health at McGill University in Montreal, Canada. “However, the results suggest that type 2 diabetics can focus on the most effective treatment pathway for their condition. Metformin does not appear to confer an increased risk of congenital malformations.”
Dr. Robert W. Platt
According to an accompanying editorial by Sarah Martins da Silva. MBChB, MD, a reproductive medicine specialist at the University of Dundee in Scotland, the Israeli findings highlight the importance of factoring the sometimes overlooked issue of paternal health into reproductive planning and prenatal care. She stressed that individual risks and benefits should always be carefully considered and results interpreted with caution since such studies lack information on glycemic control. “Nonetheless, these recent analyses suggest that metformin is a safe and effective treatment option for T2D for men and women trying to conceive as well as for managing hyperglycemia in pregnant women in the first trimester,” she wrote and agreed that it may be time to reconsider current prenatal care guidelines that advocate switching to insulin therapy.
Dr. Sarah Martins da Silva
The studies by Dr. Chiu and Dr. Rotem were funded by the National Institutes of Health. Dr. Chiu and Dr. Rotem had no competing interests to declare. Dr. Hernandez Diaz, a coauthor on both studies, reported funding from Takeda and consulting for Moderna, Johnson & Johnson, and UCB. Several authors reported support from government and not-for-profit research funding agencies. Dr. Platt disclosed no competing interests. Editorial commentator Dr. Martins da Silva disclosed consulting, speaking, travel, and advisory fees from, variously, Dyneval, Ferring Pharmaceutical, Merck, IBSA, and Gedeon Richer.