Most of us think little of inflammation until we're injured, when swelling, redness and pain flood the affected area. Even then, we focus mostly on the pain, not the internal healing process. Your body's defense mechanism kicks in, and you don't have to think too much about inflammation -- it's just there when you need it.
But inflammation might also occur when you don't need it, and that can cause problems. In some individuals, inflammation is present at very low levels. Many experts now believe this type of low-grade, chronic inflammation is responsible for a litany of chronic conditions.
"When inflammation spreads to the pancreas, you get diabetes. When it spreads to the immune system, you get cancer," says Barry Sears, an epidemiologist and best-selling author of " The Zone," an anti-inflammatory nutrition book. And like cancer, he says this type of inflammation grows and spreads, damaging organs and causing all kinds of trouble.
When inflammation spreads, it not only damages your organs, but also interferes with your brain's signals to the rest of your body. With many conditions, the trouble starts in the hypothalamus, Sears says.
"That's the command center of the brain, and it receives all these hormonal inputs that tell you when you're tired or when to eat, and what to do with those calories," he says.
When you have inflammation, proteins called pro-inflammatory cytokines distort those hormonal signals. As a result, inflammation might be causing conditions such as depression and obesity, which were correlated through research long before inflammation became a suspected culprit.
In depression, those cytokines "communicate with the brain to induce different depressive symptoms, such as sad mood, fatigue, altered sleep and social-behavioral withdrawal," says George M. Slavich, an assistant professor of psychiatry and biobehavioral sciences at the University of California-Los Angeles.
Inflammation drives obesity in a similar manner, though it's more complex and involves a third condition.
Inflammation has recently been linked with metabolic syndrome, which is a cluster of symptoms that raise your risk for chronic conditions such as heart disease, stroke and diabetes. Those symptoms include hypertension, low levels of HDL (good) cholesterol, above-normal blood glucose and triglyceride levels, and a large waist.
Most people with metabolic syndrome are obese and inactive, so these symptoms have become associated with obesity. However, many obese people don't have those symptoms. They fall into a category called metabolically healthy obese, Sears says.
"It means they don't look very good in a swimsuit, but if you look at their blood, they're in pretty good shape," Sears says. Because they probably don't have chronic inflammation, he adds, "We can't say that obesity causes inflammation, but we can say that inflammation drives obesity."
Depression is No Simpler
Slavich says inflammation may drive depression in a similar fashion.
"Links between inflammation and depression are complex, and we are just now beginning to understand how they affect each other," Slavich says. Though it's possible depression may lead to changes that cause inflammation, "experimental studies have shown that increases in inflammation can promote depression."
A study out this year made headlines for doing just that. Canada's Centre for Addiction and Mental Health published a study in January that showed people with depression had 30 percent higher levels of inflammation in the brain. It was one of the first studies to show concretely that inflammation is present in depression, even when other conditions are absent.
Still, depression is complex and unlikely to be caused by inflammation alone, just like obesity.
"When I started my career, I generally thought about depression as a psychiatric disorder or a mental health problem," Slavich says. "Most people still think of it this way. What I have come to realize is that depression is also a disorder with deep biological roots. It is as much of a physical issue as a mental one, and we should start talking about it that way."
For instance, compare depression to a more physical illness. When you have the flu, your body's immune system springs into action to fight it off, including increasing inflammation. In addition to the nausea and fever, you also have symptoms of depression: fatigue, aches, mental fog and an unwillingness to leave the house. In a contagious illness, those symptoms help us rest and avoid spreading the disease, but in depression they're nothing but trouble.
Tests that indicate your levels of inflammation are available, but they can be expensive and aren't always conclusive. They almost certainly aren't covered by insurance unless you have an autoimmune disorder.
So you may never know your true levels of inflammation, but you can still do your part to control it. Controlling inflammation is a balancing act. "You need some, but not too much. By far, the best drug we have for this is diet," Sears says.
Certain staples of the recent American diet promote high levels of inflammation. The two largest culprits, Sears says, are omega-6 fatty acids and insulin spikes brought on by consuming starchy carbs.
"The combination of insulin and omega-6 fatty acids is like a match and gasoline -- you get an explosion of this low-level inflammation," he says.
To reduce it, the best foods are those with omega-3 fatty acids and high levels of polyphenols, the compounds in fruits and vegetables that give them color. These good fats and colorful fruits and vegetables, along with lean protein, make up the majority of his anti-inflammatory meal plan.
Along with diet, a healthy lifestyle and stress-reduction techniques help reduce levels of inflammation, especially in the brain.
"It's important to maintain a healthy diet, stay active, keep a regular sleep schedule and limit the psychological stress we experience," Slavich says.
In other words, treat your mind and your body well, and they will thank you.