Depression's cognitive cost

photo of a woman pointing to a date on a calendar while looking puzzled

Elaine's memory lapses seemed minor, but they happened often. She frequently forgot where she parked her car or why she walked into a room; reminiscing with a good friend, she could barely remember a wondrous vacation the two had shared in their 40s. Now in her mid-60s — and with a mother with Alzheimer's disease — Elaine fretted that these memory blanks signaled she, too, was developing dementia.

But the true culprit was a lot sneakier: longstanding depression. A battery of cognitive tests ruled out dementia, easing Elaine's mind but provoking distress that a condition characterized by persistent sadness and apathy could also steal her ability to recall simple details.

"Few things are as depressing and anxiety-provoking as being aware you're having memory lapses or being afraid you might develop dementia," says Dr. Andrew Budson, a lecturer in neurology at Harvard Medical School who conducted Elaine's cognitive tests.

Inattention a factor

An estimated 21 million American adults — roughly 8% — have experienced at least one episode of depression, and women are twice as likely as men to have the condition, according to the National Institute of Mental Health.

Most people associate depression with its hallmark symptoms, which include not only sadness and apathy, but also loss of enjoyment in things that previously brought pleasure, appetite changes, and trouble sleeping. Yet memory is often a casualty as well, with research suggesting that having depression increases a person's risk for memory problems. Depressive symptoms can even speed memory decline in older people, according to a study of 8,200 adults published online June 11, 2024, by JAMA Network Open.

Dr. Budson points out that memory glitches common in depressed people are a byproduct of an overstimulated mind. "I think of these more as attention deficits than memory deficits," he says. "If someone has depression, they always have something on their mind that prevents them from focusing their full attention on where they are and what they're doing."

Indeed, just getting through the day can feel exhausting when you're depressed. But an inability to drum up energy and attention is only one contributor to depression-fueled memory problems, Dr. Budson says. It's believed that depression also alters levels of brain chemicals that help us focus, such as dopamine and norepinephrine. Memory issues may also stem from other depression-related changes in the brain involved in creating, combining, and recalling memories.

How dementia is distinct

Importantly, however, memory problems show up in depression quite differently than in Alzheimer's and other forms of dementia.

Someone who's depressed, for example, is likely to have a harder time retrieving long-ago memories — like the camping trip her family took when she was 8 — than remembering what she ate for breakfast that morning. A person with dementia, on the other hand, can typically summon memories from many years ago with ease, but can't recall where she went yesterday.

That's because dementia damages the hippocampus, a brain structure in charge of helping us learn new information and retrieving recent memories. We don't need the hippocampus to retrieve older memories, though, which is why people with Alzheimer's have less difficulty recalling their childhood or early adulthood.

"People with Alzheimer's can remember things that happened 20, 30, and 50 years ago quite well, at least in the early stages of the disease, but have great difficulty remembering things that happened that morning or yesterday or last week," Dr. Budson says. "The pattern is almost the exact opposite of what you see in depression."

Positive memories fade first

Another curious distinction in depression-related memory problems is how the mood disorder doesn't target all memories in the same way. Often, the first to fade are recollections of happier times — just when that type of boost would be especially welcome. Why? Again, brain biology is the culprit: areas that process positive or rewarding experiences are disrupted in people with depression.

Many, if not most, memories are context-dependent, Dr. Budson explains. Case in point: visit the town where you grew up or your old high school, and "all of a sudden you'll be able to retrieve memories you didn't even know you still had," he says.

But this type of context-dependent memory retrieval doesn't just involve places—it's also relevant for moods. "When you're feeling happy, you're more likely to be able to easily retrieve memories of other times when you were feeling happy," he explains. "And when you're depressed, it's easy to retrieve memories of other times when you were feeling depressed, but difficult to retrieve those from when you were feeling happy."

This unlucky phenomenon might make it more difficult to recover from depression, creating a vicious cycle. "It's hard to remember those happy times — and that you can be happy again," Dr. Budson says. "I don't know if that worsens depression, but it makes it hard to get out of it."

Proactive steps

Dr. Budson offers these strategies to lower your risk of depression and protect your memory if you're prone to the mood disorder:

Get your heart pumping. Regular aerobic exercise, such as brisk walking, biking, or swimming, not only generates feel-happy endorphins, but also increases growth factors in the brain that help produce new cells in the hippocampus.

Stay socially engaged. Spending time with friends and family and engaging in social activities may not only stave off depression, but also help ease it. "Being around people you like and who like you is super-helpful," he says.

Plan around your triggers. Hard experience may have taught you that certain people, places, or events can trigger your depression to recur. Avoid those situations as much as you can, and consider alternative actions during happier moments, when you have the mental bandwidth to plan ahead.

Keep your "happy people" on speed dial. Many of us have a special someone — perhaps a friend, relative, or religious adviser — who can lift our spirits on the bleakest days. Reach out to that person if you find yourself in emotional quicksand. To help you remember to do that, add reminders to your phone or calendar.

Log your favorite memories. Knowing it's normal to have difficulty summoning up pleasant memories when you're depressed, post a written list of some of your favorites on a bulletin board or refrigerator. "When you're feeling blue, read the list," Dr. Budson says. "It might just make you smile."

Common infection's dark side: Could it trigger Alzheimer's?

Being infected with Helicobacter pylori—a stomach bacterium found in an estimated two-thirds of the world's population—may be linked to an increased risk of Alzheimer's disease in adults 50 and older, a new study suggests.

Passed from one person to another, H. pylori is often harmless. But it can lead to indigestion, ulcers, and (in rare cases) stomach cancer. Alzheimer's may join that list, according to the study, which was published in the March 2024 issue of Alzheimer's and Dementia.

Researchers analyzed medical records spanning nearly three decades from more than 4.2 million people in the United Kingdom ages 50 and up. None of the participants had been diagnosed with Alzheimer's at the study's start. People with a symptomatic H. pylori infection had 11% higher odds of developing Alzheimer's disease over an average follow-up period of 11 years, the study found.

The findings are only observational and therefore do not prove that H. pylori causes dementia. But the possibility doesn't surprise Dr. Andrew Budson, a lecturer in neurology at Harvard Medical School. "We've known for more than 10 years that other infections are also associated with a higher risk of Alzheimer's disease," he says.

How might infections be linked to Alzheimer's? Research increasingly suggests that beta-amyloid—a type of protein involved in Alzheimer's-related brain plaques— is normally deposited in the brain to help it fight off infection, Dr. Budson says. But some people, due to genetic or other factors, aren't able to clear this protein out of the brain after the threat has passed.

"We all make a bit of amyloid during the day, and when we sleep at night, it gets flushed away," he says. "That's why it's important to get a good night's sleep. But over a lifetime, people sometimes generate a little too much amyloid or have trouble clearing it away. When too much of it builds up, that's what leads to Alzheimer's."