The number of deaths due to neurological disorders such as Alzheimer's, Parkinson's disease, stroke and epilepsy has increased globally by over 36 per cent in the past 25 years, according to a study published in The Lancet journal.

Neurological disorders (NDs) are the leading cause of death and disability in the world today, said Vasily Vlassov, Professor at National Research University Higher School of Economics in Russia.

In 2015, they ranked as the leading cause group of DALYs (disability adjusted life years), comprising 10.2 per cent of global DALYs, and the second-leading cause group of deaths, comprising 16.8 per cent of global deaths.

The most prevalent neurological disorders were tension- type headaches (about 1,500 million cases), migraine (about 1,000 million), medication overuse headaches (about 60 million), and Alzheimer's disease and other dementias (about 46 million cases).

Between 1990 and 2015, the number of deaths from neurological disorders increased by 36.7 per cent, and the number of DALYs by 7.4 per cent.

One of the main reasons for the increase in neurological disorders is longer life expectancy.

People live longer and, accordingly, suffer dementias more often than several decades ago, Vlassov said.

Another reason is a growing population. The more people, the more diseases are registered.

Considering the number of cases per 100,000 people, there is a positive tendency - age-standardised rates of deaths and DALYs caused by NDs decreased by 26 and 29.7 per cent respectively between 1990 and 2015, researchers said.

Stroke and communicable neurological disorders were responsible for most of these decreases, in addition to improved life standards, health care and medicine research development.

"But communicable neurological disorders in low-income countries are replaced by chronic NDs in the high-income ones. Death rates are falling, while the burden of non-mortal sufferings in a long life with a disease grows," said Vlassov.

The rates of cases per 100,000 people increased in such diseases as Parkinson's (by 15.7 per cent), Alzheimer's (2.4 per cent), motor neuron disease (3.1 per cent), and brain and nervous system cancers (8.9 per cent).

Neurological diseases are widespread both in high-income and low-income countries.

High-income countries, as well as Latin American countries have the lowest rates of DALYs (less than 3,000 per 100,000 people) and deaths (less than 100 per 100,000) due to ND, researchers said.

The highest rates (over 7,000 and over 280 per 100,000 people respectively) were estimated for Afghanistan and several African countries.