Between Saturdays
This week: how vitamin D intersects with chronic pain, how PFAS disrupt breast milk, how oral bacteria may shape mental health, and what long COVID is revealing about women’s immune systems.
This week, I kept thinking about exposure—not the dramatic kind, but the slow, everyday kind that builds in bodies over time. A missing nutrient, a plastic coating, a microbe in the mouth, and a virus that never fully leaves.
Let’s get into it.
Caught My Eye…
Vitamin D Deficiency and Chronic Pain: A Nationwide Pattern with a Gendered Reality
A cross-sectional study of over 350,000 adults in the UK Biobank, published via the International Association for the Study of Pain, has revealed a consistent association between low serum vitamin D levels and chronic musculoskeletal pain. The link was strongest in older adults and women. Researchers adjusted for dozens of confounders—including physical activity, comorbidities, and socioeconomic status—yet the correlation held. Those with vitamin D levels below 25 nmol/L were significantly more likely to report long-term pain, particularly in the back, neck, shoulders, and joints. The findings highlight how vitamin D, often seen as just a bone-health nutrient, may play a key role in the complex biology of pain—possibly through its modulation of inflammation, immune response, and neuromuscular sensitivity.PFAS and Breast Milk: A New Generational Threat
A large-scale Swedish cohort study published in Environmental Health Perspectives has shown that exposure to PFAS (per- and polyfluoroalkyl substances), the so-called “forever chemicals,” is now measurably altering breast milk composition. The most affected samples had significantly reduced fat content and altered immune components. Since breast milk is not just nutrition but a child’s first immune education, this shift raises alarm. PFAS exposure during pregnancy and breastfeeding was also associated with higher infant weight gain and early metabolic dysregulation—both early risk factors for chronic disease. The study adds to growing evidence that PFAS—ubiquitous environmental chemicals found in water, food packaging, and household products—can interfere with maternal-infant health during critical windows, with possible long-term effects on immune development and disease susceptibility.Oral Microbiome and Mental Health: Your Mouth Might Be Talking to Your Brain
A recent study in Nature Mental Health found that disruptions in the oral microbiome—the ecosystem of bacteria living in our gums, tongue, and teeth—may influence anxiety and depression risk. Using saliva samples from over 2000 adults, researchers mapped bacterial diversity and correlated it with psychiatric questionnaires and neuroimaging data. Certain bacterial strains (like Fusobacterium nucleatum) were associated with elevated inflammation markers and reduced connectivity in brain regions linked to mood regulation. The findings suggest that dysbiosis in the mouth may contribute to neuroinflammation and altered brain activity—adding a new dimension to the growing field of microbiome-mental health research that has, until now, largely focused on the gut.Long COVID in Women: A Pattern of Immune Exhaustion
Researchers at UCSF studying over 200 adults with long COVID found that women made up the vast majority of cases and showed a distinct biological signature marked by elevated immune activation, persistent viral antigens, and disrupted stress hormone levels. The study, published in Cell Reports Medicine, revealed that many women with long COVID had reduced cortisol—known as the body’s primary stress buffer—alongside increased levels of immune proteins typically seen in chronic viral infections. These changes were not seen in women who recovered normally. The findings point to a sex-specific, biologically rooted pattern of long COVID that aligns with how the immune and endocrine systems differ by gender. For the women experiencing ongoing fatigue, dizziness, and brain fog months after infection, the symptoms aren’t just lasting—they’re measurable, cellular, and rooted in a kind of immune exhaustion that science is only beginning to understand.
Until next Saturday,
Summaya