Our Brains Are Shrinking, and What Can We Do about It?

Our brains have been shrinking. Over the past 20,000 years, we've lost about 1500 cubic centimetres of brain volume, and one of the brain regions that is most susceptible to shrinkage is the hippocampus. The hippocampus is an important structure for learning and memory, including spatial memory, for decision-making, for emotional processing, and for maintaining cognitive health as we age. 

Key Takeaway

Our brains have been shrinking over the past 20,000 years and the brain region most susceptible to shrinkage is the hippocampus, a structure important for learning and memory, including spatial memory, for decision-making, for emotional processing, and for maintaining cognitive health as we age. But, there is evidence that we may continue to grow new neurons - or brain cells - throughout our lifetime. And lifestyle (diet, exercise, sleep, stress) is important for growing new neurons and for overall brain health.

There are simple lifestyle changes that we can make to reduce our risk of dementia and disability in later life. These include managing blood pressure controlling cholesterol, keeping blood sugar normal, getting physically active, eating a healthy diet, losing extra weight, quitting smoking, maintaining social relationships, and managing depression and hearing loss.

The hippocampus is remarkably plastic, with new neurons being added constantly throughout our lifetime. This is called neurogenesis and is important for maintaining cognitive flexibility and adapting to cognitive and emotional challenges. 

However, whether the hippocampus continues to add new neurons in adulthood is not without controversy. Some studies have found that neurogenesis continues throughout our lifetime, whereas other studies have estimated that adults add only 0.004%, or 1 in 25,000, of new neurons each day. This does seem negligible, but it translates into about 15% over a decade! That's why it's important to encourage neurogenesis.

But a new study that looked at the brains of 58 deceased people between the ages of 43 and 97, specifically the hippocampus, found that people keep making new brain cells throughout life, at least until age 97, and that the number of new cells tailed off with age.

Lifestyle plays an important role in adult neurogenesis and overall brain health. 

Neurogenesis Is Modulated by Lifestyle

Stress has been shown to strongly inhibit adult neurogenesis, which may lead to cognitive impairment, depression, and other psychological disorders. But not all stress is bad and it can even build resilience without affecting, and even encouraging the growth of hippocampal neurons.

Physical exercise has a strong impact on the production and survival of new hippocampal neurons and is able to overcome the negative effects of stress on neuron growth. It promotes healthy aging, improves cognitive functioning, and reduces risk of dementia. 

Diet has been strongly linked to longevity and brain aging. A healthy diet can resolve depression. Calorie restricted diets activate the production of new cells in the hippocampus. High fat diets decrease adult neurogenesis. And both of these are related to increased and decreased memory function, respectively. Some recent research is finding that our brains are starting to grow again, most probably due to better nutrition.

The research linking lifestyle to cognitive and psychological health today, and to healthy aging is overwhelming. It turns out that lifestyle factors may also encourage the growth of new neurons. 


McAuliffe, K. (2011). If moderns humans are so smart, why are our brains shrinking? Discover Magazine, January 19, 2011

Moreno-Jiménez, E., Flor-Garcia, M., Terreros-Roncal, T., et al. (2019). Adult hippocampal neurogenesis is abundant in neurologically healthy subjects and drops sharply in patients with Alzheimer’s disease. Nature Medicine, 25, 554-560.

Snyder, J. (2019). Recalibrating the Relevance of Adult Neurogenesis. Trends in Neurosciences, 42, 3.

Valero, J., Paris, I., & Sierra, A. (2016). Lifestyle Shapes the Dialogue between Environment, Microglia, and Adult Neurogenesis. ACS Chemical Neuroscience7(4), 442–453.

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  • Dear Dr. Irena, Good Wishes, Thanks for sending a thought-provoking article.We can definite restore the health and vigor of our brains.There is little awareness regarding brain health in my country INDIA.I am going through each article sent by you.

    IQBAL M.M INDIA iqbalprofessoreng@gmail.com

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