MS risk is shaped by geography, not just genes

Lack of Vitamin D seems to be one major factor fueling MS risk

Researchers believe that a combination of factors can elevate MS risk, including a lack of vitamin D exposure in different locales, genetic history, cigarette smoke exposure, and Epstein-Barr virus infection.

See MS prevalence by region in the United States

This map underscores that people in the northeastern United States have more cases of the disease as compared to the south, west, and midwest. On an individual level, these numbers may still differ based on genetic makeup and other factors irrespective of where people live.

Winter-risk SAD is more likely in regions above 40 degrees latitude north

Using latitude, depression prevalence, and populations of women and those aged 18-30, this map shows the risk of experiencing seasonal affective disorder during the winter. Researchers weighted latitude most (50%) and demographics least (5% each for women and young adults). Overall risk is not a useful predictor of prognosis for an individual.

Cigarette smoke exposure boosts MS risk by up to 55%, though smokeless tobacco doesn't

The components of the smoke itself are associated with these significantly increased risks, so it's something beyond nicotine itself that drives that risk. What's more, smoking also increases the risk of developing antibodies to MS-treating drugs.

MS can damage the brain up to 7 years before symptoms appear

Recent research scouring blood samples from 134 people with MS, both before and after their diagnosis, found that about seven years before these patients were diagnosed, there was a spike in a protein called myelin oligodendrocyte glycoprotein—indicating disease-associated damage to the protective myelin around nerve fibers.

MS Drugs reduce inflammation, helping reduce relapses and slow disease progression

Disease-Modifying Drugs calm the body's inflammatory response to help stave off relapses—when new or existing MS symptoms show up for a day or longer. Avoiding smoking, exercising, reducing stress via mindfulness, checking for vitamin D deficiencies, drinking more water and eating well, all can slow disease progression. [The jury's still out on if HRT around the time of menopause may reduce dementia risk](https://www.thelancet.com/journals/lanhl/article/PIIS2666-7568(25)00122-9/fulltext) Estrogen can reduce inflammation and support neural growth in the brain, and some research has suggested that beginning hormone replacement therapy around menopause—versus later in life—reduces Alzheimer's disease risk. Still, a recent systematic review concluded that taking HRT didn't affect dementia risk, regardless of when women started taking it, so the science remains unsettled.

Even if you have some ASD-linked gene variations you may not develop ASD

Individual environment and life experiences affect how genes perform in the body, potentially adding methyl groups to DNA that affect their function and turning genes on and off—which may heighten or reduce disease risk.

Caucasians are at the greatest risk of developing macular degeneration

A 2016 analysis across ethnic groups found, among other things, that white participants had the highest incidence of the disease, followed by Chinese, Hispanic, and Black participants. This study did not answer why that may be the case.

Females are diagnosed with MS roughly 3 to 4 times more often than males

This PBS documentary traces a filmmaker's personal journey with MS after being diagnosed at age 26. It encompasses both his efforts to stymie the disease's progression and his search for answers about the disease, when, statistically, he seemed at low risk due to his gender, lack of known family risk, and other factors.

People with blue eyes appear to be at elevated risk of developing macular degeneration, perhaps because more light can penetrate their eyes.

Stroke risk doubles each decade after age 55

While age is the greatest risk factor, genetics, diet, and overall health play a prominent role in determining individual stroke risk. Prevention focuses heavily on modifiable risk factors. High blood pressure is the single most important controllable risk factor, contributing to both types of stroke.

Alzheimer's in the United States is most prevalent in the South and the East.

MS disproportionately sickens women, but men tend to have worse outcomes

Though the disease is more common in women, men's symptoms progress more quickly, with men more often diagnosed with progressive MS and men's cases typically resulting in more severe symptoms—perhaps due at least partly to more delayed diagnosis—and more severe disability over time.

Environmental determinism links human traits and societal progress to geography

Also known as climatic determinism, the theory states that the latitudes where people are located influence their emotional and intellectual capabilities. Originating in Ancient Greece, these ideas were used throughout history to justify racial hierarchies.

Epstein-Barr virus—the cause of 'kissing disease' mononucleosis—may be the leading cause of MS

A Harvard study with data from more than 10 million US military personnel found that people that contracted Epstein-Barr virus had a roughly 32-fold increased risk of developing multiple sclerosis. The work, published in 2022, found that Infection of the virus preceded MS onset by a median of five years, raising questions about better Epstein-Barr virus management and potential disease prevention.

Twin studies helped scientists understand why mosquitoes like some of us more than others

A combination of carbon dioxide output, skin chemistry, genetic factors, hormones, and clothing choice can make us particularly vulnerable to mosquito bites. Watch how mosquitoes responded to one man in the video versus his wife, a research approach typically conducted with identical and fraternal twins to test mosquito attractiveness.

A vaccine against Epstein-Barr virus, researchers hypothesize, could potentially prevent MS

As many as a quarter of MS patients have antibodies in their blood that bind to both a central protein in Epstein-Barr virus and a protein made in the brain and spinal cord that—when attacked—leads to a breakdown of protective nerve fiber insulation. This suggests the immune system's primed to attack the nervous system after mounting a defense against Epstein-Barr.

Read a study about racial differences in Lyme disease diagnosis

The research published in September 2025 examined differences in Lyme disease diagnosis among Medicaid and Medicare beneficiaries using data from 2016 to 2021. It notes that though US Lyme disease surveillance data indicates more than 90% of diagnosed Lyme cases are among white people, people of color—particularly those who identify as Black or African American—have higher rates of more severe disease of Lyme, with symptoms including arthritis and neurologic impacts.

Changes in vision or eye pain can be early MS symptoms

This occurs due to myelin degradation around the optic nerve, impairing its ability to transmit visual information to the brain. Individuals may especially experience eye symptoms after exercising or taking a hot shower because boosted body temperatures slow down nerve function in nerves already damaged by MS.

More than 20 mosquito-borne and tick-borne diseases are found in the US

Children, older adults, and people with compromised immune systems are at particular risk of poorer health outcomes from these diseases. But dog owners and outdoor enthusiasts are among those at particular risk of contracting these illnesses, which include Lyme disease, Zika, and the condition Alpha-gal Syndrome.

Climate determinism wrongly linked human traits and societal progress to geography

Historically rooted in Greek philosophy, its ideas used the latitudes where people were located to justify racial hierarchies, casting tropical peoples as lazy or inferior. These biases still influence how media and research portray people in climatically disadvantaged regions. (Some readers may experience a paywall.)

Environmental conditions, shifting immunity, and viral strain could help explain 2025 spike

The surge in HFMD in the summer and early fall of 2025 in the mid-Atlantic could be the result of a confluence of factors, including a more virulent strain of disease-causing virus, good environmental conditions for the virus to spread—hot, humd—and a potential immunity gap among kids due to milder HFMD outbreaks the previous year.

There are multiple types of multiple sclerosis—they differ by attack patterns

When your immune system targets the nervous system, this can cause new or worsening symptoms and the development of scarring or damage within the central nervous system. Relapsing-remitting MS is the most common type of the disease—it includes progressive bouts of attacks that occur months or years apart.

Multiple sclerosis means 'many scars'

That's a reference to the scarring or lesions that occur in the brain, spinal cord, and elsewhere whenever the immune system has a flare-up. The immune system attacks the myelin because it incorrectly responds as if it's a threat, damaging the body's ability to transmit electrical signals effectively from areas of the body to the brain.

Learn how your earwax may be determined by genetics—and geography

Researchers have discovered that wet and dry earwax are associated with specific gene variations. Wet earwax is particularly associated with warmer areas of Europe, Asia, and the Americas, suggesting that dry earwax may have been evolutionarily advantageous in cooler climates.

Risk factors linked with ASD include older parents, preterm births, and toxic prenatal exposures

Though researchers agree that there is a strong genetic component to ASD development, certain environmental factors heighten that risk, with studies suggesting older parents, premature birth, maternal obesity, and air pollution exposure in utero all elevate risks of ASD development. There is no connection between receiving vaccines and ASD development.

How reading and writing can lower dementia risk by almost 40%

Research published in 2026 that tracked almost 2,000 older adults for an average of nearly eight years suggests that lifelong exposure to intellectual stimulation, such as learning a language, reading, and writing, can lower dementia risk by as much as 40%.

80% of schizophrenia cases may be inherited

Some research suggests that anywhere between 60% and 80% of people with schizophrenia had genes that predisposed them to the syndrome. That high rate has fueled interest in further exploration of what environmental and lifestyle factors cause some people with that genetic risk to develop the disease when others with the same genetic risks do not.

Some data links schizophrenia to older paternal age and birth complications

Yet both associations are not yet considered firm enough to definitively be causative. Schizophrenia is a multi-causal syndrome and a mixture of factors, including genetics, are widely believed to be behind its development.

Minorities are largely underrepresented in medical research, which compromises our understanding of how conditions and treatments may affect various populations, but recent efforts, like the African Ancestry Neuroscience Research Initiative and new genome research studies, are seeking to close that gap.

Multiple genes are associated with Alzheimer's risk, but one particularly well-known disease-associated gene is apolipoprotein E (APOE), which typically encodes a protein that helps carry cholesterol and other fats in the bloodstream.

US macular degeneration burden is based on statistical modeling and Medicare claims

Prevalence estimates for age-related macular degeneration in the US are usually based on the Vision and Eye Health Surveillance System. Disease numbers are generated using Bayesian meta-regression (a type of statistical modeling), which pulls together information from multiple sources, including Medicare claims.

Vitamins can slow macular degeneration

Research published in 2022 affirmed that vitamin formulations containing vitamins C and E, copper, zinc, lutein, and zeaxanthin—but no beta carotene—can enhance eye health and slow the progression of macular degeneration.

Cancer rates are on the rise among GenXers and Millennials

Cancer rates are rising among Gen X and Millennials, with more cancer diagnoses being made in their 30s and 40s than previous generations. Factors such as prenatal exposures, environmental toxins, and lifestyle choices may contribute to this trend. Memorial Sloan Kettering Cancer Center's experts discuss these issues, exploring how these insights could reshape cancer risk understanding.

Why genetic testing for Alzheimer's risk may not be right for you

Medical experts warn that completing Alzheimer's testing for late-onset versions of the disease can be fraught, in part because there's a shortage of genetic counselors to help navigate the findings and their potential implications, including for one's finances. Learning you have one or two copies of the APOE4 gene variant, which elevates Alzheimer's risk, can be panic-inducing, but an elevated risk for the disease is not the same as saying it definitely will develop.

Autoimmune disease prevalence and incidence are on the rise—but no one knows why

Researchers theorize that environmental factors, including shifts to less healthy diets, air pollution, infections, stress, climate change, and exposures to xenobiotics—substances like pesticides, plastics, and toxins that incite immune responses—may all be fueling epigenetic changes to our bodies that make people's immune responses go awry.

10 percent of SAD cases occur in the summer

Despite its significantly lower incidence, summer-risk SAD is as significant as its winter counterpart. Rather than being prompted by less light, the summer version is typically spurred by high temperatures, strong light, distinct summer time social pressures (appearing in a bathing suit, for example), and pollen. Common treatments include keeping cool and prioritizing sleep.

Sitting 10+ hours per day increases dementia risk

People who sit for at least 10 hours per day are more likely to develop dementia, according to a study published in 2023. This article details the study on the murky relationship between brain health and prolonged sitting. This study involved...