A higher death rate in 2015 can be attributed to three main causes, but many of those deaths could have been prevented.

It’s not our hearts or even gun violence.

It’s drugs, depression, and one form of dementia.

Following years of decline, the death rate in the United States rose in 2015.

Preliminary data from the National Center for Health Statistics (NCHS) reveals the main reasons for the increase were drug overdoses, suicide, and Alzheimer’s disease.

There was only a slight increase in deaths attributed to heart disease.

The death rate, adjusted for age, went from 724 deaths per 100,000 people in 2014 to 729 in 2015. The last increase was in 2005, mainly due to a particularly bad flu season.

“We are not accustomed to seeing death rates increase on a national scale,” Andrew Fenelon, Ph.D., researcher at the Centers for Disease Control and Prevention (CDC) told The New York Times. “We’ve seen increases in mortality for some groups, but it is quite rare to see it for the whole population.”

It’s too early to say whether it’s a one-year blip or the start of a trend, but experts say there’s a lot we can do to improve those numbers.

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Many drug overdoses involve prescription drugs.

Part of the problem lies in the prescribing habits of physicians, driven in part by patient demand, according to family physician Dr. Philip Caravella.

“Physicians need more training in how to manage pain,” he told Healthline. “It’s probably too easy to prescribe opioids when other medications might be helpful.”

Over time, people develop a tolerance to opioids. To achieve the desired effect, you have to keep increasing the dose.

The big problem is that opioids affect the part of the brain that controls breathing, said Caravella.

“Ultimately, people die because they stop breathing,” he said.

Using sedatives or alcohol while taking opioids increases the risks.

A drug called naloxone can save people from respiratory death due to opioid overdose if it’s injected in time.

Caravella suggests a potential lifesaving solution, if medical and legal consequences could be worked out. That would be to allow physicians to issue a prescription for naloxone to a family member of long-term opioid users.

Physicians need better education about how to use these drugs, said Caravella.

“We also need to lower the risk of malpractice or negligence for physicians who are working with patients and providing appropriate warnings and instructions,” he said.

Street drugs are another problem.

Heroin overdoses keep increasing, said Caravella. It’s easy to overdose when you have no way of knowing the product’s potency.

“The problem with street drugs is not going away with our current system,” he said. “We have to look at this realistically. If we have legislation to legalize, you can reduce availability on the street. The potency would be established in production, so you’re less likely to overdose. Legalization of many of these substances is probably the way to go.”

“Overdosing on drugs is more common than being killed in a car accident,” he added. “We have to stop ignoring it and looking the other way and pretending it will get better. Big problems require big decisions.”

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According to Caravella, suicide is one of the most difficult problems to anticipate.

“Ninety percent who do commit suicide have psychiatric disorders such as depression, anxiety, bipolar disorder, alcoholism, etc. The suicide rate is highest among the poorest and least educated people, as well as among the highest educated. Either extreme is higher,” said Caravella.

For every successful suicide, there are many more failed attempts. The only predictable thing about suicide is that one attempt means you’re likely to attempt again.

“Some research shows that a person can be too depressed to attempt suicide,” Caravella explained. “When they start to get better, they’re sometimes more able to complete the act. There’s a fine line between treatment and benefits. Everything is a lot more complicated than it appears.”

We have a poor handle on prevention and need a lot more research, according to Caravella. He also notes that suicide is a difficult problem to research.

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While the number of people dying from Alzheimer’s disease is going up, Michael Harrington, M.B., Ch.B., F.R.C., said that’s because we’re living longer.

“When corrected for age, the prevalence is decreasing and has done since the 1930s,” Harrington, director of neurosciences at Huntington Medical Research Institutes (MHRI), told Healthline.

Harrington said there’s currently no treatment known to slow or halt the progression of Alzheimer’s disease. That doesn’t mean there’s nothing we can do.

He said many of the efforts to reduce the deaths from cardiovascular diseases — still the biggest killer in the United States — involve the same risk factors for Alzheimer’s disease.

“We need to publicize them to reduce Alzheimer’s disease,” said Harrington. “These include having good annual physician checkups and advice, stopping smoking, treating high blood pressure, high blood lipids, and high blood sugar.”

He advises good lifestyle habits such as exercising cognitively and physically, reducing stress, and nurturing good social behaviors.

He’d also like to see boxing and other activities that cause brain trauma made illegal or minimized to cut down on brain trauma.

Harrington also stresses a concentration on health rather than on disease, since prevention is much easier and less expensive than treatment.

“The important need is for a lot more research to seek an understanding of the neurodegeneration process that is occurring decades before any symptoms. HMRI and some other organizations are actively following this urgently needed approach,” said Harrington.

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Caravella, who is also a weight loss expert and author of “Weight No Longer: The Prescription for Amazing Fitness & Living,” believes the biggest health issue of all is obesity and other weight-related problems.

He’s been studying the cause and effect of obesity for 20 years and said it contributes to a host of health problems.

It’s the number one cause of type 2 diabetes. It also increases the risk of many cancers as well as cardiovascular diseases.

These health problems and their associated costs could be dramatically reduced if people understood the importance of fitness and normal weight, according to Caravella.

Processed foods are a huge problem, he said.

“Our diet should be made up of foods that exist in nature,” he commented.

He’d like to see nutrition education and daily physical education added to every child’s curriculum, beginning in kindergarten.

A healthy diet is important, but Caravella said it’s more of an exercise and fitness problem than an eating problem. Our sedentary lifestyle is at fault and exercise is the remedy.

Caravella has a few more suggestions for avoiding unnecessary health problems. Don’t smoke. Wear your seatbelt. And protect your skin from the sun’s harmful rays.

“Medicine is offtrack. After all my years of practicing, I’m looking at things differently than I used to. We’ve made great strides in diagnosis and treatment. But we need to start preventing, so we don’t have to diagnose and treat.”