Nervous System Disorders Now Top Global Health Threat

The Number One Thing That Disables Humanity Is Not What You Think

For decades, heart disease reigned as the world’s top cause of health loss. Cancer was close behind. Then came stroke, lower respiratory infections, and the familiar litany of killers that dominated public health headlines. But in 2021, something shifted. According to the most comprehensive analysis of neurological health ever conducted, disorders affecting the nervous system now collectively account for more disability and premature death than any other category of disease. The authors of this study, led by Jaimie D. Steinmetz and colleagues at the Institute for Health Metrics and Evaluation, calculated that these 37 conditions caused 443 million disability-adjusted life years (DALYs) in 2021. That is a measure of total health loss, combining years lost to early death with years lived with disability. No other group of diseases came close (Steinmetz et al., 2024).

This is not a niche finding. It is a reordering of global health priorities. The authors found that 3.4 billion people, or 43.1 percent of the world’s population, were living with a nervous system disorder in 2021. That is nearly half of everyone on Earth. And the burden is growing: total DALYs increased by 18.2 percent between 1990 and 2021 (Steinmetz et al., 2024).

But here is the part that surprised me. The age standardized death rate from these conditions actually dropped by 33.6 percent over that same period. People are living longer with neurological damage, not dying from it. That is good news, but it also means we are facing a massive and growing wave of chronic neurological disability that most health systems are not prepared to handle.

Why This Study Is Different From Every Previous One

Previous global burden estimates for neurological conditions looked at only 15 disorders. They excluded neurodevelopmental conditions like autism spectrum disorder. They ignored the neurological consequences of infections like COVID-19, malaria, and Zika. They did not account for diabetic neuropathy, which turned out to be the fifth leading cause of neurological health loss worldwide.

Steinmetz and her team expanded the scope to 37 conditions. They did something methodologically clever: instead of lumping all cases of a disease like preterm birth into the neurological category, they conducted a sequela level analysis. That means they looked at the specific health outcomes of each condition and only counted the cases where actual nervous system damage occurred. A baby born preterm who develops cerebral palsy counts. A baby born preterm who grows up healthy does not. This is not a trivial distinction. It means the numbers in this study are more precise than anything that came before (Steinmetz et al., 2024).

The authors used data from 204 countries and territories, spanning 1990 to 2021. They estimated mortality, prevalence, years lived with disability (YLDs), years of life lost (YLLs), and DALYs, broken down by age and sex. They applied a comorbidity correction to avoid double counting people who have multiple neurological conditions. This is epidemiology at its most rigorous.

The Top 10 Conditions That Are Reshaping Global Health

The authors ranked conditions by age standardized DALYs in 2021. Here is the list, and it contains some surprises.

• ▸Stroke: Still the single largest contributor, but its burden is shifting from high income countries to low and middle income ones.
• ▸Neonatal encephalopathy: Brain damage in newborns, often due to oxygen deprivation during birth. This is a massive problem in parts of Africa and South Asia.
• ▸Migraine: Third place. Migraine is not just a headache. It is the leading cause of years lived with disability among people under 50.
• ▸Alzheimer’s disease and other dementias: Rising fast as populations age, but the age standardized rate is actually declining in some high income countries.
• ▸Diabetic neuropathy: This is the shocker. Nerve damage from diabetes now ranks fifth. The global diabetes epidemic is driving this.
• ▸Meningitis: Still a major killer in children, especially in the meningitis belt of sub Saharan Africa.
• ▸Epilepsy: A condition that is highly treatable but remains stigmatized and under treated in many parts of the world.
• ▸Neurological complications due to preterm birth: As more preterm infants survive, more are living with long term neurological damage.
• ▸Autism spectrum disorder: The first time this has been included in a global burden analysis at this scale.
• ▸Nervous system cancer: Brain and spinal cord tumors round out the top ten.

What stands out is the diversity. Stroke and dementia are diseases of aging. Migraine and epilepsy strike young adults. Neonatal encephalopathy and preterm birth complications affect the very youngest. Diabetic neuropathy is a complication of a metabolic disease that is skyrocketing worldwide. The nervous system is vulnerable at every stage of life, and the threats are multiplying (Steinmetz et al., 2024).

The COVID-19 Complication Nobody Is Talking About

The study includes COVID-19 as one of the infectious diseases that can cause neurological damage. The authors isolated cases where the virus led to cognitive impairment or other nervous system sequelae. This is a relatively new addition to the burden, and it is not yet fully understood.

The authors found that the age standardized prevalence of nervous system disorders was almost stable between 1990 and 2021, changing by only 1.5 percent. That might seem like good news, but it masks a critical shift. The total number of people affected is rising because the population is growing and aging. The proportion of people with these conditions is not changing much, but the absolute number is exploding.

COVID-19 added a new layer. The authors note that post COVID cognitive impairment, often called brain fog, is now a recognized neurological condition. The long term burden of this is unknown. If even a small fraction of the hundreds of millions of people infected with SARS CoV 2 develop persistent cognitive symptoms, the neurological burden will increase substantially in the coming years.

How Much of This Is Preventable?

This is where the study gets uncomfortable. The authors calculated risk factor attributable burden for several conditions. Stroke, for example, is heavily driven by high blood pressure, smoking, and diet. Diabetic neuropathy is a direct consequence of poorly managed diabetes. Neonatal encephalopathy is often preventable with better obstetric care. Meningitis can be prevented with vaccines.

But the authors also point out that for many neurological conditions, the risk factors are not well understood. Migraine has genetic and environmental triggers that are still being mapped. Alzheimer’s disease has a complex interplay of age, genetics, and lifestyle factors that we are only beginning to untangle. Autism spectrum disorder has known genetic components, but environmental contributions remain controversial.

The authors found that age standardized death rates from neurological conditions dropped by 33.6 percent between 1990 and 2021. That is a massive improvement. It means we are getting better at keeping people alive after stroke, meningitis, and brain injury. But age standardized DALYs dropped by only 27.0 percent. The gap between these two numbers is the disability burden. We are saving lives, but we are not saving function. People are surviving neurological events only to live with chronic disability.

The Geography of Neurological Suffering

The study breaks down burden by region and country, and the disparities are stark. High income countries have lower rates of stroke and meningitis but higher rates of Alzheimer’s and diabetic neuropathy. Low income countries, especially in sub Saharan Africa and South Asia, bear a disproportionate burden of neonatal encephalopathy, meningitis, and epilepsy.

The authors found that the ten conditions with the highest age standardized DALYs in 2021 included several that are almost entirely preventable with existing interventions. Neonatal encephalopathy can be reduced with better monitoring during labor. Meningitis can be prevented with vaccines. Diabetic neuropathy can be prevented with early detection and treatment of diabetes.

But prevention requires health systems that function. It requires access to prenatal care, vaccines, and diabetes management. In many parts of the world, those systems do not exist. The authors note that the global burden of neurological disorders is not just a medical problem. It is a political and economic one.

What This Study Does Not Tell Us

No study is perfect, and the authors are transparent about their limitations. The 37 conditions they included do not cover everything that can go wrong with the nervous system. They excluded chronic pain conditions that are not clearly neurological, even though pain is processed by the nervous system. They excluded psychiatric disorders like depression and anxiety, even though these have neurological underpinnings. The boundary between neurology and psychiatry is artificial, and this study reinforces it.

The data quality varies enormously by region. For many low income countries, the authors had to rely on sparse data and statistical modeling. The uncertainty intervals for some conditions are wide. The authors report 95 percent uncertainty intervals for their estimates, and for some conditions in some regions, those intervals are large enough to make you hesitate before quoting the numbers as gospel.

The study also does not tell us why the burden is shifting. It documents the change but does not explain the causes. Is the increase in diabetic neuropathy purely due to rising diabetes rates, or are there other factors at play? Is the decline in age standardized stroke burden in high income countries due to better blood pressure control, or to something else? The authors identify risk factors for some conditions but not for others. The mechanisms remain unclear.

What This Actually Means

The takeaway from this study is not that we should panic about neurological disease. It is that we should rethink our priorities. Here is what the findings demand.

• ▸Health systems need to integrate neurology into primary care. Most neurological conditions are managed by specialists, but there are not enough neurologists in the world, especially in low income countries. Migraine, epilepsy, and diabetic neuropathy can be treated by general practitioners if they are trained to recognize them.
• ▸Prevention of neurological disability is possible and cost effective. Stroke prevention through blood pressure control is one of the best public health investments available. Diabetes prevention prevents neuropathy. Vaccines prevent meningitis. The tools exist. They are just not being deployed everywhere.
• ▸The global burden of neurological disease is not just about aging. Neonatal encephalopathy and preterm birth complications affect the youngest. Migraine and epilepsy affect working age adults. This is a life course problem, not just a geriatric one.
• ▸We need better data. The uncertainty in these estimates is a call for better surveillance, not a reason to dismiss the findings. Countries that do not track neurological conditions cannot manage them.
• ▸The definition of neurological disease is expanding. Post COVID cognitive impairment is a new addition. As we learn more about how infections, toxins, and metabolic disorders affect the brain, the list of conditions that count as neurological will grow. This study is a snapshot, not a final verdict.

Steinmetz and her colleagues have done something important. They have shown that nervous system disorders are not a niche concern. They are the dominant cause of health loss in the world today. The question now is whether our health systems, our research funding, and our political will are ready to meet that reality.