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No, normal adults don’t lose 100,000 brain cells a day, and dementia not inevitable

“You lose 100,000 brain cells every day,” claims a message posted on “FACTS SA”, a public South African Facebook group with some 180,000 followers. It’s been viewed more than 113,000 times since it was posted on 21 February 2022. 

This number sounds alarming, but what does it really mean to lose brain cells? And is the message true?

BrainCells_Incorrect

Concepts of ‘brain cell’ and ‘loss’ not that simple 

Apart from cells associated with blood vessels, there are two main types of cell in the brain – neurons and glial cells. 

Neurons act as messengers in the brain, using chemical signals and electrical impulses to send information between brain areas and between the brain and the rest of the body. 

Glial cells used to be thought of as simply the “glue” holding the nervous system together. But glia actually play other important roles in the brain, such as communicating with neurons and each other, and supporting neuron function. 

Scientists used to think that in the average adult brain, glial cells outnumbered neurons by 10 to one. But over the last decade, new research and innovation in the ways brain cells are counted suggests that the actual number of glia is around 50 to 60 billion. The number of neurons in an adult brain is roughly 100 billion. So how does loss of these cells work?

The loss of brain cells is not as simple as the message suggests. Most neurons are not replaced after they die, but glial cells are regularly replenished. 

Africa Check spoke to neuroscientist Christopher von Bartheld from the US University of Nevada, Reno, who has written extensively on cell death. He explained that around a quarter of all microglia, which make up about 10% of the glial cells in the brain, are replenished every year. 

“When you do the maths, that means that each day about 4 million microglial cells die. But they are replenished, so there is a loss, but no ‘net loss’,” he told us.

Neuron death common early in life – but not inevitable in old age

As for neurons, substantial loss is not common in people’s lives. The two exceptions are at the beginning and, sometimes, nearer to the end of life. 

When the brains of mammals such as people are developing, double the number of neurons are made than are actually preserved. Around half of all neurons die off before and shortly after birth. If the number lost in this process was averaged throughout the entire human lifespan, this would equal far more than 100,000 neurons lost per day, Von Bartheld told us. 

Neurodegenerative diseases, which usually occur in old age, may also cause substantial neuron death. The diseases include Parkinson’s and Alzheimer’s. Von Bartheld said the brain could lose many more than 100,000 neurons a day in patients with these diseases. Damage from a stroke or physical trauma can also cause neuron death.

But apart from normal neuron loss at and before birth, and loss from neurodegenerative diseases, the death of neurons is not as common as it was once thought to be. 

The idea that people normally lose neurons comes from old studies from the 1950s to 1980s, which suggested that after the age of 30 the normal brain loses large numbers of neurons every day. 

Scientists used to believe that this cell death was what caused dementia, which was therefore seen as an inevitable part of ageing. But studies like these were flawed, and today research suggests that there is “very little if any normal loss of neurons in most parts of the brain”. 

This is good news, because it means the cognitive decline that comes with dementia is not an unavoidable part of growing old, as was once believed.

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