The hippocampus, a pair of small curved structures deep in the brain that help form new memories, gets slightly smaller in nearly everyone as they age. Illness, heavy drinking, poor sleep, and other everyday health problems can make it shrink faster.1PubMed. A systematic review and meta-analysis of longitudinal hippocampal atrophy in healthy human ageing Unlike most of the brain, though, the hippocampus keeps making new nerve cells in adulthood, which is part of why some of the loss can be slowed or partly won back.2PubMed. Adult Neurogenesis in the Human Dentate Gyrus Whether shrinkage can be reversed depends less on how much was lost than on what caused it.
How Much Shrinkage Is Normal With Age
On MRI reports, doctors call loss of brain volume “atrophy.” Healthy adults lose an average of about 0.85% of hippocampal volume a year.3PubMed. A systematic review and meta-analysis of longitudinal hippocampal atrophy in healthy human ageing The rate depends on age: about 0.4% a year before 55, about 1% from 55 to 70, and about 1.1% after 70.4PubMed. A systematic review and meta-analysis of longitudinal hippocampal atrophy in healthy human ageing People who start with a smaller hippocampus also tend to lose volume a bit faster afterward.5PubMed Central. Lower hippocampal volumes at baseline are associated with higher volume loss in healthy elderly
A loss of around 1% a year is spread over many years and is usually too small to notice day to day. Most people feel no change in memory from it. Everyone also starts from a different baseline, so two healthy 70-year-olds can have noticeably different hippocampal sizes without either having a disease.
Large charts built from nearly 20,000 healthy people let doctors compare one scan to others of the same age.6PubMed Central. Hippocampal volume across age: Nomograms derived from over 19,700 people in UK Biobank People with Alzheimer’s often fall below the bottom 5% of healthy people their age.7PubMed Central. Hippocampal volume across age: Nomograms derived from over 19,700 people in UK Biobank That’s why a report saying “volume normal for age” is reassuring, while one far below age norms needs follow-up.
Mild loss described as “age-appropriate” usually reflects normal aging, not disease. A single scan shows size, not speed; only repeat scans show how fast the hippocampus is changing. If your report mentions volume, ask the doctor whether the finding is in line with your age.
Alzheimer’s Disease and Faster Shrinkage
In Alzheimer’s, an abnormal protein called tau (which spinal fluid and PET tests can measure) first collects in a memory region right next to the hippocampus, then spreads into it.8Alzheimer’s & Dementia. Early stages of tau pathology and its associations with functional connectivity, atrophy and memory Only later does it reach the outer brain areas involved in language and spatial sense.9Alzheimer’s & Dementia. Early stages of tau pathology and its associations with functional connectivity, atrophy and memory Even in people with no memory problems yet, more tau is linked to more local shrinkage.10Alzheimer’s & Dementia. Early stages of tau pathology and its associations with functional connectivity, atrophy and memory So hippocampal shrinkage can begin years before symptoms.
Early on, people often notice trouble recalling recent conversations, repeating questions, or misplacing things more than before, while older memories stay intact. The hippocampus helps form new memories, so damage there hits learning new information before it erases long-held memories like childhood events.
Once Alzheimer’s is established, higher tau in spinal fluid predicts faster hippocampal shrinkage afterward.11PubMed Central. Baseline CSF p-tau levels independently predict progression of hippocampal atrophy in Alzheimer disease Mild cognitive impairment (MCI), memory problems that don’t yet affect daily life, often shows volumes between the bottom 5% and 25% for age.12PubMed Central. Hippocampal volume across age: Nomograms derived from over 19,700 people in UK Biobank Mild memory problems don’t always progress to Alzheimer’s. Some people stay stable and a few improve, especially when a treatable cause is found.
Shrinkage alone can’t diagnose Alzheimer’s, because many causes in this article shrink the hippocampus. Doctors combine scans with memory tests and sometimes spinal fluid or PET tests for tau and amyloid. A scan that looks normal for age alongside memory complaints may point instead to sleep, mood, or other causes.
Blood Pressure, Diabetes, and Sleep Apnea
In older adults with mild memory problems, higher top-number blood pressure is linked to faster hippocampal shrinkage.13PubMed Central. High blood pressure predicts hippocampal atrophy rate in cognitively impaired elders A wider gap between the top and bottom numbers shows the same link.14PubMed Central. High blood pressure predicts hippocampal atrophy rate in cognitively impaired elders
The hippocampus is packed with insulin receptors.15PubMed Central. Brain Atrophy in Type 2 Diabetes When the brain becomes resistant to insulin in type 2 diabetes, it may struggle to use sugar for energy and shrink preferentially.16PubMed Central. Brain Atrophy in Type 2 Diabetes Chronically high blood sugar also creates by-products that drive inflammation and damage to tau protein.17PubMed Central. Brain Atrophy in Type 2 Diabetes
People with memory impairment and obstructive sleep apnea have smaller hippocampi than those without it, even after accounting for weight, blood pressure, and diabetes.18PubMed Central. Examining the association between sleep apnea and total hippocampal volumes in cognitive impairment In people with only self-noticed memory worries, the difference wasn’t found.19PubMed Central. Examining the association between sleep apnea and total hippocampal volumes in cognitive impairment Repeated drops in oxygen during sleep can damage the hippocampus’s memory cells through chemical stress and inflammation.20PubMed Central. Chronic intermittent hypoxia and obstructive sleep apnea: an experimental and clinical approach
Signs of sleep apnea worth raising with a doctor include loud snoring, gasping, or pauses in breathing that a partner notices. Waking unrefreshed and feeling sleepy during the day despite enough hours is another. A sleep study can confirm it, and treatment like CPAP keeps oxygen steady overnight.
These are among the most controllable causes, because blood pressure, blood sugar, and apnea can all be measured and treated. If a scan shows faster-than-expected loss, ask for these checks.
For blood pressure, a single clinic reading can mislead because nerves or rushing can raise it. Home readings taken at rest on several days give a truer picture. Sit quietly for a few minutes, keep your arm supported at heart level, and record both numbers. Treatment decisions depend on the pattern over time, so bring the log to appointments rather than changing medication on your own.
Alcohol and Head Injury
People with problem drinking have smaller hippocampi on average.21PubMed Central. Problematic alcohol use and reduced hippocampal volume: a meta-analytic review Animal experiments show alcohol itself can shrink it.22PubMed Central. Problematic alcohol use and reduced hippocampal volume: a meta-analytic review In people, though, a naturally smaller hippocampus might also make problem drinking more likely.23PubMed Central. Problematic alcohol use and reduced hippocampal volume: a meta-analytic review In teens with alcohol use disorders, starting younger and drinking longer go with a smaller hippocampus.24PubMed. Hippocampal volume in adolescent-onset alcohol use disorders
Recovery is the harder part. In one group of people who stopped drinking, hippocampal volume did not recover.25PubMed Central. Genetic and Behavioral Determinants of Hippocampal Volume Recovery During Abstinence from Alcohol Damage may be permanent after years of drinking, especially combined with smoking.26PubMed Central. Genetic and Behavioral Determinants of Hippocampal Volume Recovery During Abstinence from Alcohol
Quitting still matters. Stopping prevents further toxic damage on top of what’s already lost, and other brain areas and memory function can improve even when hippocampal size doesn’t. Because starting young seems to raise the stakes, cutting back earlier helps more.
Traumatic brain injury shrinks the hippocampus on both sides.27PubMed. Hippocampal head atrophy after traumatic brain injury The loss mostly hits the front part.28PubMed. Hippocampal head atrophy after traumatic brain injury Compared with uninjured people, though, the average shrinkage is modest.29PubMed Central. Hippocampal volume in normal aging and traumatic brain injury
Helmets for cycling and contact sports reduce injury risk. Older adults most often injure their heads in falls, so fall-proofing the home matters. If memory problems linger after a concussion, tell a doctor.
Stress, Inflammation, and Menopause
Long-lasting high levels of stress hormones reduce new nerve cell growth and weaken connections in the hippocampus.30PubMed Central. Stress effects on the hippocampus: a critical review Memory problems and anxiety- or depression-like behavior can follow, at least in animals.31PubMed Central. Stress effects on the hippocampus: a critical review Much of this is a pulling-back of nerve cell branches, not cell death, so it can reverse.32PubMed Central. Chronic Stress-Induced Hippocampal Vulnerability: The Glucocorticoid Vulnerability Hypothesis Easing chronic stress removes the trigger so branches can regrow, which is why treating depression or PTSD is part of protecting memory. Timing matters, though: in rats, severe trauma in adolescence left fewer, shorter branches into adulthood.33Frontiers in Cell and Developmental Biology. Long-Term Effect of Post-traumatic Stress in Adolescence on Dendrite Development and H3K9me2/BDNF Expression in Male Rat Hippocampus and Prefrontal Cortex
Inflammation elsewhere in the body sends signals that activate the brain’s immune cells.34PubMed Central. Chronic Peripheral Inflammation, Hippocampal Neurogenesis, and Behavior Those cells slow the birth and survival of new hippocampal neurons.35PubMed Central. Chronic Peripheral Inflammation, Hippocampal Neurogenesis, and Behavior In animals, ongoing gut inflammation cut the production of new hippocampal neurons.36PubMed Central. Chronic intestinal inflammation alters hippocampal neurogenesis Autoimmune diseases like lupus and multiple sclerosis can shrink the hippocampus too.37Cureus. Cognitive Decline in Chronic Inflammatory Conditions: Exploring Links Between Systemic Inflammation and Neurodegeneration
Falling estrogen during perimenopause is linked to about a 2.8% loss in hippocampal volume, along with more inflammation.38PubMed. Estradiol reduction during perimenopause is associated with lower BDNF, elevated inflammation, hippocampal loss, and cognitive decline Hormone therapy isn’t a simple fix, though. Women aged 71 to 89 who had taken horse-derived estrogen therapy in a trial had smaller hippocampi than those on placebo.39PubMed Central. Estrogens, hormone therapy, and hippocampal volume in postmenopausal women So starting hormone therapy late in life is not a way to protect the hippocampus. Women weighing hormone therapy should discuss timing and type with their doctor, since memory protection alone isn’t an established reason to start it.
Can the Hippocampus Grow Back
One part of the adult hippocampus holds stem cells that produce new working neurons.40PubMed. Adult Neurogenesis in the Human Dentate Gyrus In rats, new neurons made up about 30% of the cells added over adulthood, and the area grew overall.41bioRxiv. The dentate gyrus grows throughout life despite turnover of developmentally-born neurons Older neurons were lost at the same time, so growth was smaller than new-cell births alone would predict.42bioRxiv. The dentate gyrus grows throughout life despite turnover of developmentally-born neurons BDNF, a brain growth protein, helps new neurons form, and stress lowers it.43PubMed Central. Exercise training increases size of hippocampus and improves memory44Frontiers in Cell and Developmental Biology. Long-Term Effect of Post-traumatic Stress in Adolescence on Dendrite Development and H3K9me2/BDNF Expression in Male Rat Hippocampus and Prefrontal Cortex
New neurons don’t simply refill what was lost. They start immature and need weeks to wire into existing circuits, so a birth counted in the lab is not the same as a working cell. Many die before they connect, so only a share end up contributing to memory. The pace of making them also appears to slow with age, which limits how much repair is available in later life. Realistically, reversal means small gains, a few percent, not a return to youth.
Exercise and Diet That Slow or Reverse Shrinkage
In older adults, a year of aerobic walking grew the front of the hippocampus by about 2%.45PubMed Central. Exercise training increases size of hippocampus and improves memory That roughly turned back one to two years of age-related loss, and memory improved along with it.46PubMed Central. Exercise training increases size of hippocampus and improves memory Larger gains came with higher levels of the brain growth protein BDNF.47PubMed Central. Exercise training increases size of hippocampus and improves memory
The walking in that kind of program was brisk enough to raise the heart rate, about 40 minutes three times a week. Starting with shorter sessions and building up over weeks is fine. Gains need ongoing exercise; stopping likely lets loss resume. Consistency matters more than the exact activity, so pick something you can do in any weather, like walking indoors or a stationary bike. Brisk means you can talk but not sing; if you could easily sing, pick up the pace.
Older adults who closely followed a Mediterranean diet lost about 2.5 fewer years’ worth of hippocampal volume over time.48Alzheimer’s & Dementia. O1‐08‐01: Mediterranean DIET is Associated with Slower Rate of Hippocampal Atrophy: a Longitudinal Study in Cognitively Normal Older Adults In people over 50, a green Mediterranean diet with exercise slowed shrinkage to 0.8% versus 1.3% on a standard healthy diet.49PubMed Central. The effect of a high-polyphenol Mediterranean diet (Green-MED) combined with physical activity on age-related brain atrophy: the Dietary Intervention Randomized Controlled Trial Polyphenols Unprocessed Study (DIRECT PLUS) More green tea, walnuts, and the leafy plant Mankai, plus less red and processed meat, were each linked to less loss.50PubMed Central. The effect of a high-polyphenol Mediterranean diet (Green-MED) combined with physical activity on age-related brain atrophy: the Dietary Intervention Randomized Controlled Trial Polyphenols Unprocessed Study (DIRECT PLUS)
In a weekly menu, that means building meals on vegetables, beans, whole grains, olive oil, and fish. Swap red and processed meat for these, add a handful of walnuts, and make green tea an easy daily habit.
Mind training may help too. Eight weeks of a mindfulness course increased gray matter in part of the left hippocampus.51PubMed Central. Mindfulness practice leads to increases in regional brain gray matter density Most studies of mindfulness find gray matter gains, though these studies are mostly small.52PubMed Central. Mindfulness Practice and Increases in Gray Matter Density, Gray Matter Volume, and Cortical Thickness: A Scoping Review Virtual reality navigation training may also help memory in people with mild memory problems.53PubMed. Effects of virtual reality-based spatial cognitive training on hippocampal function of older adults with mild cognitive impairment
Alzheimer’s Drugs and Shrinking on Scans
Some older experimental Alzheimer’s drugs sped up hippocampal shrinkage by about 20% beyond placebo.54PubMed Central. Accelerated Brain Volume Loss Caused by Anti–β-Amyloid Drugs Amyloid-clearing antibodies enlarged the brain’s fluid spaces.55PubMed Central. Accelerated Brain Volume Loss Caused by Anti–β-Amyloid Drugs With lecanemab, though, a drop in hippocampal volume may reflect cleared swelling and fluid, not nerve damage.56PubMed Central. Lecanemab treatment modulates brain volume and cerebrospinal fluid pathways in early Alzheimer’s disease: Insights from longitudinal magnetic resonance imaging
MRI measures volume, which includes water, so clearing swelling or fluid from tissue can make the hippocampus look smaller without nerve cells being lost. With the older drugs, faster shrinkage was a real concern and not simply a fluid effect.
If you’re on lecanemab or a similar drug, expect regular MRI checks for swelling side effects. A smaller hippocampus on follow-up may not mean the drug is failing, so ask the specialist how they interpret volume changes on treatment.
Can Dehydration Skew Your Scan
In healthy older adults, subtle dehydration was strongly linked to a smaller measured hippocampus.57PubMed Central. Precisely-Measured Hydration Status Correlates with Hippocampal Volume in Healthy Older Adults Drying out and rehydrating can change measured brain volume by about 0.4%.58PubMed Central. Correlation between brain volume change and T2 relaxation time induced by dehydration and rehydration: Implications for monitoring atrophy in clinical studies Other day-of factors, like heart rate and blood pressure, showed no effect on hippocampal volume.59PubMed Central. Impact of physiological factors on longitudinal structural MRI measures of the brain So drink normally before a scan, especially if it will be compared to an earlier one.
Drink fluids as you normally would the day before and the morning of the scan, unless the instructions say otherwise, such as fasting for contrast. Avoid extremes like a long sweaty workout or heavy alcohol the night before, since these can leave you dehydrated. If you take water pills or have kidney or heart conditions, follow your doctor’s fluid advice instead of drinking extra.
When comparing two scans, small changes near 1% can fall within normal measurement noise. Using the same scanner and method makes comparisons more trustworthy. Ask whether a change is larger than the expected measurement error.