Neurological conditions now leading cause of ill health and disability globally: Lancet study

New Delhi: Neurological conditions such as epilepsy, Alzheimer's disease and dementia are now the leading cause of ill health and disability globally, affecting 3.4 billion people in 2021, according to a major new analysis published in The Lancet Neurology journal.

Globally, the number of people living with, or dying from, neurological conditions such as stroke, Alzheimer's disease other dementias, and meningitis has risen substantially over the past 30 years. This is due to the growth and ageing of the global population as well as increased exposure to environmental, metabolic, and lifestyle risk factors, the researchers said.

The study suggests that worldwide, the overall amount of disability, illness, and premature death -- a measurement known as disability-adjusted life years (DALYs) -- caused by neurological conditions increased by 18 per cent over the past 31 years, rising from around 375 million years of healthy life lost in 1990 to 443 million years in 2021.

The analysis from the Global Burden of Disease, Injuries, and Risk Factors Study (GBD) 2021 shows that the absolute number of DALYs is increasing in large part due to ageing and growing populations worldwide.

The top 10 contributors to neurological health loss in 2021 were stroke, neonatal encephalopathy (brain injury), migraine, Alzheimer's disease and other dementias, diabetic neuropathy (nerve damage), meningitis, epilepsy, neurological complications from preterm birth, autism spectrum disorder, and nervous system cancers, the researchers said.

Neurological consequences of COVID-19 (cognitive impairment and Guillain-Barre syndrome) ranked 20th, accounting for 2.48 million years of healthy life lost in 2021, they said.

The most prevalent neurological disorders in 2021 were tension-type headaches (around 2 billion cases) and migraines (about 1.1 billion cases). Diabetic neuropathy is the fastest-growing of all neurological conditions, the researchers said.

"The number of people with diabetic neuropathy has more than tripled globally since 1990, rising to 206 million in 2021," said study co-senior author Liane Ong from the Institute for Health Metrics and Evaluation (IHME), University of Washington, US.

"This is in line with the increase in the global prevalence of diabetes," Ong said in a statement.

The research builds on previous GBD studies to provide the largest and most comprehensive analysis to compare the prevalence and burden of nervous system disorders between countries on a global scale between 1990 and 2021.

"Every country now has estimates of their neurological burden based on the best available evidence,” said study lead author Dr. Jaimie Steinmetz from IHME.

"As the world's leading cause of overall disease burden, and with case numbers rising 59 per cent globally since 1990, nervous system conditions must be addressed through effective, culturally acceptable, and affordable prevention, treatment, rehabilitation, and long-term care strategies," Steinmetz said.

Over 80 per cent of neurological deaths and health loss occur in low- and middle-income countries (LMICs), the researchers said.

Overall, estimates reveal striking differences in nervous system burden between world regions and national income levels, they said.

The study shows that in high-income Asia Pacific and Australasia -- regions with the best neurological health -- the rate of DALYs and deaths were under 3,000 and 65 per 100,000 people, respectively in 2021.

In these regions, stroke, migraine, dementia, diabetic neuropathy, and autism spectrum disorders accounted for most health loss, it found.

In the worst-off regions of western and central sub-Saharan Africa, the rate of DALYs and deaths were up to five times higher (over 7,000 and 198 per lakh people respectively) in 2021, with stroke, neonatal encephalopathy (brain injury), dementia, and meningitis the biggest contributors to years of healthy life lost.

"Nervous system health loss disproportionately impacts many of the poorest countries partly due to the higher prevalence of conditions affecting neonates and children under 5, especially birth-related complications and infections," said Tarun Dua, Head of WHO's Brain Health unit and one of the co-senior authors of the study.

"Improved infant survival has led to an increase in long-term disability, while limited access to treatment and rehabilitation services is contributing to the much higher proportion of deaths in these countries," Dua said.

The researchers highlight that, as of 2017, only a quarter of countries globally had a separate budget for neurological conditions, and only around half had clinical guidelines.

The analysis suggests that modifying 18 risk factors over a person's lifetime --most importantly, high systolic blood pressure -- could prevent 84 per cent of global DALYs from stroke.

Estimates also suggest that controlling lead exposure could reduce the burden of intellectual disability by 63 per cent while reducing high fasting plasma glucose to normal levels could reduce the burden of dementia by around 15 per cent.