How recognizing biological differences between males and females is transforming research and medicine
In the sprawling landscape of scientific research, a critical variable has been systematically overlooked for decades: biological sex. While decades of advocacy have pushed for the inclusion of women in clinical trials, a startling 2025 study reveals that inclusion alone does not ensure sex differences are meaningfully addressed in research 4 .
The analysis of over 94,000 COVID-19-related publications found that a mere 4% examined sex or gender-specific health considerations 4 .
of studies examined sex differences
This neglect has grievous implications for advancing equitable healthcare, reinforcing a one-size-fits-all approach to medicine that fails to address unique health needs across populations 4 .
"Drug development pipelines increasingly incorporate information on genetic differences in protein levels and function," making understanding population differences, including those between sexes, essential for precision medicine approaches .
— Professor Claudia Langenberg, Queen Mary University of London
This article explores how recognizing sex differences is transforming scientific understanding and paving the way for more effective, personalized healthcare for everyone.
Refers to the classification of living things as male, female or intersex, based on reproductive anatomy, chromosomes, and hormone profiles.
Encompasses socially constructed roles, behaviors, and identities. In rigorous scientific studies, data is typically categorized based on chromosomal information (XX or XY) .
The biological differences between males and females extend far beyond reproductive systems. A landmark 2025 study published in Nature Communications analyzed the genetic links between approximately 6,000 proteins and hundreds of diseases in 56,000 males and females.
The team discovered that for two-thirds of these proteins, their levels differed between males and females .
of proteins show sex-based differences
These protein variations influence nearly every bodily system, from how we metabolize medications to how our brains respond to stress.
Surprisingly, only about 100 proteins out of the 6,000 studied showed differences in the genetic 'switches' controlling their levels when comparing males and females . This indicates that while profound biological differences exist between the sexes, what causes these differences isn't solely down to genetics.
Non-medical factors such as work environment, education, financial situation, access to resources, and lifestyle also significantly contribute to the health differences observed between the sexes .
A groundbreaking study led by researchers at the University of Florida Health provides a compelling example of how sex differences manifest at the molecular level. Published in Science Advances in early 2025, this research explored why males and females experience stress differently 6 .
The team investigated the brain's production of a neurosteroid called allopregnanolone (AP), which is crucial for regulating the body's response to acute stress. AP helps boost focus and energy during stressful events, enabling effective response to challenges. The production of AP relies on an enzyme called 5α-reductase (5αR), which exists in two main forms: 5αR1 and 5αR2 6 .
Journal: Science Advances
Year: 2025
Institution: University of Florida Health
Focus: Stress response mechanisms
The researchers designed a series of experiments using laboratory rats to examine the role of these enzymes in stress response:
Researchers exposed both male and female rats to controlled stressful stimuli and measured subsequent changes in enzyme levels and AP production.
Using advanced techniques, the team identified where in the brain these enzymes were most active, focusing on the prefrontal region known for executive functions and stress regulation.
The researchers experimentally reduced 5αR2 levels in male rats to observe behavioral changes in response to stress and rewarding stimuli.
To confirm the enzyme's role, they administered AP to rats with reduced 5αR2 and observed whether this restored normal stress response capabilities.
The study revealed striking sex-based differences in stress response mechanisms. Acute stress was found to raise levels of 5αR2—but not 5αR1—in the front region of the brain of male laboratory rats. Female rats, however, showed no such change, highlighting a significant sex-specific difference in how stress may be managed at the molecular level 6 .
| Aspect Measured | Male Rats | Female Rats |
|---|---|---|
| 5αR2 change under stress | Significant increase | No significant change |
| 5αR1 change under stress | No significant change | No significant change |
| Behavior after 5αR2 reduction | Less engaged, slower response | Not tested |
| AP administration effect | Restored response ability | Not tested |
Table 1: Key Findings from Stress Response Study 6
When researchers reduced 5αR2 in male rats, these animals became less engaged and slower to respond to both acute stress and rewarding stimuli. However, administering AP restored this ability, underscoring the enzyme's critical role 6 .
"Men, in general, tend to have a greater propensity to display outward, aggressive reactions to acute stress, whereas women have a much greater tendency to internalize their responses. This distinction is believed to contribute to the higher female prevalence of anxiety and depression" 6 .
— Marco Bortolato, Senior Author
The implications of sex differences extend far beyond stress response, influencing diverse areas of health and medicine:
Research presented at the 2025 New Trends in Sex Differences and Women's Health Research conference revealed that biological sex influences how foods taste and how nutrients are processed 1 .
The same research highlighted important considerations for women's heart health. Nitric oxide, a signaling molecule essential for normal heart function, declines over time in women along with estrogen 1 .
Research has uncovered sex-specific responses to mineral deficiencies. Zinc deficiency, for example, has been found to raise blood pressure and harm kidney health in both sexes, but males show more severity in their symptoms 1 .
| Biological Process | Female Pattern | Male Pattern | Health Implications |
|---|---|---|---|
| Fat taste sensitivity | Higher sensitivity | Lower sensitivity | May contribute to postmenopausal weight gain in women |
| Nitric oxide production | Declines with estrogen | Less affected by age | Higher heart disease risk in postmenopausal women |
| Zinc deficiency effects | Moderate severity | Greater severity | More pronounced hypertension and kidney issues in men |
Table 2: Sex Differences in Nutritional Biology 1
Studies found that estrogen makes taste cells respond more strongly to fatty acids, making females more sensitive to the taste of fat and potentially causing them to eat less of it. This sensitivity decreases in males, which may help explain why they generally eat more fat 1 .
These findings have particular relevance for menopause care, as declining estrogen levels may reduce fat taste sensitivity, potentially contributing to postmenopausal weight gain 1 .
While sex differences in biology are increasingly recognized, gender disparities within the scientific community itself remain problematic. A systematic comparison of gender inequality in scientific rankings across disciplines analyzed over 80 million papers published from 1975 to 2020.
The findings revealed that women remain a minority in all 19 fields studied, with physics, geology, and mathematics having the lowest percentage of papers authored by women at 14%, while psychology had the largest percentage at 39% 9 .
lowest female representation (physics, geology, mathematics)
More troubling is the significant underrepresentation of women in top-ranking positions. Women were consistently underrepresented in the top 10% or higher across all fields and metrics, including productivity (number of papers), research impact (citations), and co-authorship networks 9 .
| Field Category | Lowest Female Representation | Highest Female Representation |
|---|---|---|
| pSTEM fields | 14% (Physics, Geology, Mathematics) | ~19% (Computer Science) |
| Social Sciences | ~30% (Political Science) | 39% (Psychology) |
| Medicine | Ranks 7th in papers with women authors | Ranks 3rd in percentage of women authors |
Table 3: Women's Representation in Scientific Fields 9
The research revealed that rankings are rigid over time, making it challenging for early-career researchers, especially women, to reach top positions. The study also found that women and men with comparable productivity levels and career age tend to attain different citation levels, with women benefiting more from co-authorships while men benefit more from productivity, especially in physical STEM fields 9 .
The growing recognition of sex differences is transforming how research is conducted across disciplines. From the lab to the clinic, scientists are developing new approaches that account for biological sex as a fundamental variable:
Encouragingly, research has demonstrated that targeted interventions can effectively address gender biases in science. A workshop called "Scientific Diversity" was administered to life science instructors as part of the National Academies Summer Institute for Undergraduate Education.
Evidence emerged indicating the workshop's efficacy—participants showed increased awareness of gender bias, expressed less gender bias, and were more willing to engage in actions to reduce bias just two weeks after participating compared to two weeks before the intervention 7 .
The scientific community is increasingly adopting methodologies that account for sex differences. This includes:
"For the first time in history, we are able to study human biology at this level of detail—across genes, proteins, and more. Our findings highlight the need to better understand the factors that impact health differences—at the genetic level and beyond—to create more tailored and equitable healthcare for everyone" .
— Dr. Mine Koprulu, Lead Author of the Protein Study
The journey to fully understanding how biological sex influences health and disease is just beginning, but the implications are already profound.
Accounting for sex differences isn't just about fairness—it's about producing better, more rigorous science.
From developing sex-specific treatments for stress-related disorders to creating personalized nutritional recommendations.
Recognizing these differences promises to revolutionize medicine and create truly personalized healthcare.
As research continues to illuminate the intricate ways biological sex shapes our health, one thing becomes increasingly certain: in the pursuit of scientific excellence, sex doesn't just matter—it's essential. The future of medicine depends on our ability to integrate this fundamental variable into every aspect of research and clinical practice, paving the way for truly personalized healthcare that meets the unique needs of all people.