MadSci Network: Cell Biology

Re: how many brain cells does an average person lose per day from the age of 30

Date: Fri Mar 15 14:43:32 2002
Posted By: Brenda Hefti, AAAS Fellow
Area of science: Cell Biology
ID: 1016103215.Cb

I had a hard time finding a clear answer on this question, so I think we 
should do the math ourselves.  Here are the facts:

Most estimates say we have about 100 billion brain cells (neurons), and 
about ten times that many, or one trillion, support cells (glia) that help 
the neurons.  We'll just concentrate on the neurons themselves.

The brain weighs about 3 pounds, and after age 20, you lose about a gram of 
brain mass per year.  Three pounds is about 1.4 kilograms (scientists work 
in the metric system, so that's the units we'll use here).

So…if the brain weighs 1.4 kilos (1400 grams) and there are about 100 
billion neurons, that comes to about 70,000,000 (70 million) neurons per 
gram.  Now we could stop here and say that we lose 70 million neurons a 
year, or about 190,000 per day, but that wouldn't really be right.  That's 
because most of that gram isn't really neurons dying.  Some of that loss is 
glia (support cells) dying, some of it is because the neurons are shrinking 
but not dying, and some of it is that the neurons lose some of their 
insulation (myelin), which makes them slower, but doesn't cause them to 

Even if we say that only 5% of the gram is neurons actually dying, we get 
neuron loss of about 9,000 neurons a day!  That seems like a lot, doesn't 
it?  But when you think about it, that's nothing compared to the number you 
have left.

A side note:  This is all assuming you're a person who takes care of 
yourself.  But there are lots of things people do that cause much higher 
rates of brain cell death.  The big one is using certain drugs.  Not all 
drugs cause brain cells to die, but the ones that do are very damaging.  
Ketamine, nitrous oxide (laughing gas) and volatile inhalants (glue, 
gasoline, paint thinner) can cause brain cell death at THIRTY TIMES normal 
rates - that's almost 300,000 neurons a day!  And alcohol also increases 
the rate of brain cell death, but less than the others.

Please contact me with any questions!


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