Nearly half of the planet suffers from a neurological disease

Neurological diseases are now the leading cause of ill health in the world. A study published in The Lancet Neurology journal has estimated that in 2021 around 3.4 billion people worldwide — 43% of the world’s population — suffered from a nervous system disorder, such as Alzheimer’s and other forms of dementia, stroke, migraine or autism spectrum disorders, among others. The study shows that, over the last three decades, the number of people living with or dying from such pathologies has increased (by 59% and 41%, respectively) due to the aging of the population and the influence of environmental, metabolic or unhealthy lifestyle factors that constitute risk factors for some of these pathologies (e.g., stroke and dementia). The authors warn of the “enormous” impact of these pathologies on public health and call for the implementation of public policies and resources to respond to the demand for care.

Neurological diseases are an amalgam of pathologies that share the common aspect of damage to the nervous system. However, these conditions are complex and widely vary in terms of diagnosis, treatment, prognosis and the healthcare they require. For example, dementia has little or nothing in common with a neurodevelopmental disorder, or a headache with motor neuron diseases such as amyotrophic lateral sclerosis (ALS). The coinciding aspect is that all of them form a category of highly prevalent pathologies that can result in a substantial loss of quality of life and length of life. According to the 2021 Global Burden of Disease (GBD) study, which quantifies the decline in health due to 371 diseases in more than 200 countries on a regular basis, neurological conditions — the study groups 37 pathological conditions within this category — caused more than 11 million deaths in 2021 and contributed to one of the largest losses in quality of life globally.

The study analyzed classic neurological pathologies, such as stroke or migraine, but for the first time it also included pathologies bordering on other areas, such as autism spectrum disorder or attention deficit hyperactivity disorder. It also includes new phenomena that have emerged in recent years, such as neurological conditions associated with Covid-19 (cognitive impairment or Guillain-Barré syndrome) or neurodevelopmental damage in infants whose mothers were infected with Zika virus during pregnancy. “We estimate that 3.4 billion people experienced some form of neurological health loss in 2021, which is a staggering number. This is largely due to certain conditions that are widespread. For example, tension-type headaches affected about 2 billion people in 2021. Our analysis takes into account independent comorbidity within conditions, which means that one individual may have more than one disease at the same time,” explains Jaimie Steinmetz, author of the study and researcher at the Institute for Health Metrics and Evaluation at the University of Washington.

In order to assess the impact on health of these conditions, researchers use disability-adjusted life years (DALYs), an indicator that measures all the time of full, healthy life lost due to disease, associated ill health or premature death. According to the study published in The Lancet Neurology, neurological diseases account for a global loss of 443 million healthy life years, which makes this group of pathologies the leading cause of ill health and disability worldwide, even ahead of cardiovascular diseases, the authors agree. Since 1990, DALYs caused by neurological diseases have increased by 18%.

“The increase in total DALYs — and the rise in the total number of people living with neurological health loss — is primarily due to the aging of the population and population growth,” Steinmetz points out. Indeed, many neurological conditions, such as dementia or Parkinson’s disease, are more common in old age. However, the author adds that, paradoxically, if the effect of demographic changes is eliminated and standardization by age is applied, the study shows that death rates in certain pathologies, such as stroke or neonatal encephalopathy, decrease: “These downward trends are fueled by improved mortality prospects, but, in addition, increased survival through better care means that we see more years lived with disability in the population. For example, more children with long-term neurological consequences.”

Poor countries are the most affected

The neurological conditions that result in the highest number of years of healthy life lost are stroke, neonatal encephalopathy, migraine, Alzheimer’s disease and other forms of dementia, and diabetic neuropathy (nerve damage associated with high blood glucose). Meningitis, epilepsy, neurological complications in premature babies, autism spectrum disorders and cancer of the nervous system are also ranked at the top of the table of pathologies most affecting quality of life. However, there are differences according to country and age.

Lower income regions are more impacted by this group of diseases. In developing territories, such as central and western Sub-Saharan Africa, neonatal encephalopathy, meningitis and neural tube defects are some of the diseases that result in the greatest loss of healthy life years, while these same pathologies in high-income regions, such as Australasia, are much less prevalent and therefore have a lesser impact. “The decline in nervous system health disproportionately affected people in low- and middle-income countries, partly due to a higher prevalence of conditions affecting newborns and children under the age of five years,” the authors of the article explain.

The condition with the most consistent impact around the globe is stroke: in 19 of the 21 regions analyzed in the study, it is the pathology that contributes most to the loss of healthy years of life. In terms of age, in children under five years old, the most common conditions are neonatal encephalitis, meningitis and neural tube defects; in children and adolescents, neurological disorders associated with prematurity and epilepsy predominate; in adults aged 20 to 59 years, stroke, migraine and diabetic neuropathy are the most common; and in the elderly, stroke is accompanied by dementia and Parkinson’s disease. This age-based diversity, according to Steinmetz, “supports the need to consider neurological health and healthcare throughout a lifetime.”

The researchers also analyzed how the impact of neurological disorders has fluctuated over the past 30 years and detected significant changes. For instance, the years of healthy life lost have soared by more than 90% since 1990 in the case of diabetic neuropathy and have decreased by the same amount with tetanus. Nevertheless, everything has an explanation: the global surge in the incidence of diabetes may account for an increase in its neurological effects and, on the other hand, the authors point to routine vaccination “for the substantial decrease in deaths due to tetanus globally.” “The promotion and implementation of folic acid supplementation and enrichment of cereal products contributed to the decrease in the incidence of neural tube defects in countries where this basic public health initiative has been institutionalized,” the researchers add.

“Fight to protect brain health”

Jesús Porta, president of the Spanish Society of Neurology, applauds the publication of this study, although he did not participate in it: “It is very interesting and important for us. Not so much for the neurologist’s everyday practice, because we already know a lot of the data, but research that shows the years of loss of quality of life due to neurological diseases warns us that we have to fight to protect brain health.” Given this scenario of rising neurological pathology, the physician calls for “health prevention campaigns and structuring of the healthcare system to ensure that there is an adequate response.” For example, he says, with specialized units to meet the growing and diverse demand.

Steinmetz also echoes this sentiment. “An aging population means more cases of conditions affecting older adults, like neurodegenerative conditions. Healthcare systems must anticipate this and ensure that treatment and care systems are in place to cope with the increasing burden.” The researcher points out that “more than 80% of neurological deaths and DALYs occur in low- and middle-income countries” and, despite these environments carrying a higher burden of disease, the workforce trained to treat these conditions is “70 times larger” in high-income areas. “This problem needs to be addressed,” he warns.

The authors also focus on preventable risk factors and stress that high blood pressure, smoking or high blood glucose levels are variables that favor neurological pathologies, such as stroke or Alzheimer’s disease. “In 2021, 84% of stroke-associated DALYs were potentially preventable if exposure to 18 identified risk factors were decreased,” the authors summarize. In this regard, Porta mentions three healthy lifestyle tips that help prevent brain pathologies: “Physical exercise, adequate sleep patterns and adequate nutrition,” he concludes.

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