Sex Differences in the Association Between Lithium Treatment and Kidney Function in Patients with and without Bipolar Disorder
This retrospective cohort study of 3,458 adults reveals that long-term lithium exposure, particularly greater cumulative use and a history of toxicity, is consistently associated with declining kidney function across both sexes and patients with or without bipolar disorder, whereas the disease itself shows a weaker association with renal changes.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
For more than seventy years, lithium has stood as the cornerstone treatment for bipolar disorder, a condition that causes severe shifts in mood and energy. It is a powerful tool that stabilizes the mind and reduces the risk of suicide, yet it carries a significant burden: the drug is processed entirely by the kidneys, and over many years, it can wear down the body's ability to filter waste. This creates a difficult balancing act for doctors and patients. They must weigh the life-saving benefits of the medication against the slow, often invisible damage it might be causing to the kidneys. While it is known that the drug can harm the kidneys, it has remained unclear exactly how much of that damage comes from the drug itself versus the underlying illness, or whether men and women experience these effects differently.
A team of researchers at the Mayo Clinic set out to untangle these complex threads by looking at the medical records of thousands of adults. They examined the kidney function of people who had taken lithium for their bipolar disorder and compared them to people who had taken the same drug but did not have the diagnosis. By tracking changes in kidney performance over time, the study aimed to separate the effects of the medication from the effects of the disease and to see if sex played a role in how the kidneys responded. The researchers focused on a specific measure of kidney health called the estimated glomerular filtration rate, which tells us how well the kidneys are cleaning the blood. They looked at how this number changed over an average of two years, paying close attention to how long people had taken the drug, whether they had ever had dangerously high levels of lithium in their blood, and their age and sex.
The study analyzed data from 3,458 adults, a large group that included both men and women with and without bipolar disorder. The researchers found that the longer a person was exposed to lithium, the more their kidney function tended to decline. Specifically, for every additional year a person took the medication, their kidney filtration rate dropped by a small but measurable amount. This decline was consistent across the board, affecting men and women alike, and it happened regardless of whether the person had bipolar disorder. The illness itself did not appear to be the primary driver of kidney damage; rather, the duration and intensity of the lithium treatment were the strongest predictors of how the kidneys fared.
A particularly important finding emerged regarding past episodes of high lithium levels. The researchers defined toxicity as having a blood concentration of lithium that reached or exceeded 1.2 millimoles per liter. When people had a history of reaching these levels, their kidney function was lower overall. However, this link was not the same for everyone. The data showed a clear association between past toxicity and reduced kidney function in women, but this connection was not statistically significant in men. This suggests that women may be more vulnerable to the lingering effects of high lithium levels, though the study did not find that men and women reacted differently to the simple passage of time on the drug.
The researchers also looked at how the kidneys changed between the first and last measurements for each person. They found that people who had been on lithium for more than two years during the study period saw a steeper drop in kidney function compared to those with shorter exposure. This pattern held true for everyone in the study, regardless of their sex or whether they had bipolar disorder. The study did not find evidence that the relationship between the drug and kidney decline was fundamentally different for men versus women, nor did it find that having bipolar disorder made the kidneys more susceptible to the drug's effects.
These results offer a clearer picture of the risks involved in long-term lithium treatment. They confirm that the drug itself is the main factor in the gradual decline of kidney function, rather than the mental health condition it treats. The findings also highlight that while the overall risk is similar for both sexes, women may face a specific vulnerability if they have ever experienced high levels of the drug in their blood. This does not mean the treatment should be abandoned, but it reinforces the need for careful, ongoing monitoring of kidney health and lithium levels, especially for women and for anyone who has been on the medication for a long time. By understanding these specific patterns, doctors can better manage the delicate balance between protecting the mind and preserving the kidneys.
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