Many people are familiar with the idea that gut bacteria are important for health. Given their location, you might assume that role is only about digestion.

But evidence is mounting that the microbes in our intestines interact with our minds – and hearts – in significant ways. Gut bacteria have been linked to depression, anxiety and the regions of the brain that process emotions. These regions share brain circuitry that affects cardiovascular issues such as blood pressure.

“People have co-evolved with environmental bacteria (that have) adapted over aeons to being at home in human bodies. The present-day result is that our metabolism, our neurons and indeed our entire physiology is an interactive cross-talk with the bacteria in our bodies,” said Bruce R. Stevens, professor of physiology and functional genomics in the College of Medicine at the University of Florida in Gainesville.

He perceives humans and gut bacteria as one interactive “meta-organism” – a single ecology of human cells plus bacterial cells.

Depression-like behaviours

The idea that guts and minds are linked goes back centuries, and the influence of gut bacteria on our health has been discussed in the press for years. But recently, after thousands of published articles, understanding of the links has grown immensely.

For example, studies show transferring gut bacteria from depressed people into lab rats can cause the rats to exhibit depression-like behaviours. Similar mouse studies show gut bacteria affect anxiety.

Dr Kirsten Tillisch, professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles, led a study in 2013 that was the first to show eating a bacteria-friendly, or probiotic, food – in this case, yoghurt – affected regions in the brain associated with processing of emotion and sensation in healthy women with no psychiatric symptoms. Four years later, her team linked specific gut bacterial profiles to brain differences in those regions.

How might tiny microbes exert such great influence? Stevens explained some basics.

First, the number of bacteria in your gut is vast – 50 trillion or so, which equals about one for every human cell in our bodies. The makeup of this bacterial collection, or microbiome, is affected by many things, including diet, exercise and cultural influences.

Those bacteria interact with the brain and other organs in three ways. First, the gut and brain communicate by molecules carried in the blood, and microbes influence those chemical messages.

Serotonin comes from gut wall

Microbes also interact with the gut’s special nervous system, called the enteric nervous system. It has a direct, two-way connection with the brain via the central nervous system.

Finally, the immune system of the gut wall and the body’s other immune components respond to gut microbes, affecting the brain and organs.

Here’s one example of how it all ties together. You might have heard of serotonin and dopamine, neurotransmitter molecules that steer mood and behaviour in brain circuits. These molecules also are found in the gut. In fact, Stevens said, most of the body’s serotonin comes from the gut wall.

Gut bacteria also use them to signal the gut’s nervous system and its direct link to the brain. The bacterial messages also can prompt responses from the body’s immune system.

Summed up: “Your gut, your brain and your immune system interact,” Stevens said. “The triangulation of those things controls much of your other physiology, whether it’s blood pressure, metabolism or mood.”

Plus, it’s two-way communication, he said. “We use their molecules; they use our molecules and physiology in a mutualistic way.” Our understanding of these interactions, he said, could someday open the door to better treatment, diagnosis and prevention for disorders of the heart and mind.

Eat more fruits and vegetables

To Tillisch, the body-brain link to the gut biome is significant not just for what it might do in the future, but for what anyone can do with it now.

“I really feel like all the research to date has pointed us to really basic concepts” that add up to “what we eat and how we live our lives is going to affect our health, whether it’s our mental health, whether it’s our cardiovascular health, whether it’s our gut health, whether it’s our neurologic health.”

She’s intrigued by the prospect that an understanding of gut bacteria might someday explain why some people can, say, eat a seemingly unhealthy food but stay thin. But for now, she said, we can use our knowledge to do what we already know is good for us – such as to avoid processed foods and eat more fruits and vegetables.

Research supports the Mediterranean diet, Tillisch said. The diet features fish and poultry, and includes plenty of fruits, vegetables, bread and other grains, potatoes, beans, nuts and seeds. It uses olive oil as a primary fat source.

Stevens agreed. “There is currently no ‘silver bullet’ probiotic or antibiotic, although certain combinations of probiotics are providing promising research results. If you want to foster ‘good guy’ bacteria over ‘bad guy’ bacteria, research evidence demonstrates the best way is to exercise and eat a diet that has the appropriate dietary fibre, unsaturated fat and low sugar, which will encourage the growth of those particular species of bacteria.”

People get excited about the microbiome, Tillisch said. “Like, ‘Oh, it’s so cool, all these things are making all these decisions and changing our health!’ They’re really resulting from our behaviours – whether we exercise, whether we take (medications), whether we drink alcohol, whether we eat well.

“And it’s really – eat well.”

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It’s widely believed that marijuana is not addictive, but a major new evidence review suggests that’s not true.

Not only can people suffer withdrawal symptoms when they quit pot, but nearly half of those who regularly or heavily use marijuana will go through withdrawal when they stop, according to the study published online on 9 April in JAMA Network Open.

About 47% of frequent users seeking treatment experience what’s dubbed cannabis withdrawal syndrome, according to pooled results from 47 studies that included more than 23 500 participants.

“The results suggest that withdrawal is likely or possible for a large majority of users, particularly heavy users,” said Emily Feinstein, executive vice president of the Center on Addiction, in New York City.

Withdrawal a real phenomenon

“People should be prepared to experience withdrawal if they are going to stop using marijuana, and ideally consult a healthcare provider to help manage the symptoms and reduce the risk of relapse,” added Feinstein, who was not involved with the study.

Marijuana withdrawal symptoms include nervousness, anxiety, sleeplessness, depression, restlessness and irritability, said Dr Timothy Brennan, director of the Addiction Institute of Mount Sinai, in New York City.

People quitting pot also might experience physical symptoms like stomach pain, shakiness, tremors, sweating, fever, chills and headaches, he said.

“It can be miserable, and presents a challenge for people trying to get sober from cannabis,” Brennan said.

Experts have long argued that marijuana withdrawal is a real phenomenon, but these concerns received a new legitimacy with the 2013 publication of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), Brennan said.

The DSM-5, considered the bible for psychiatric diagnoses, recognised cannabis withdrawal syndrome as a bona fide disorder.

More common in men

Brennan, who was not involved with the study, said it’s likely that withdrawal is occurring more often because today’s pot is much more potent than before.

“The cannabis supply that’s out there now compared to the cannabis supply that was around in the 1960s and 1970s shows a dramatic increase in the percent of THC,” the chemical in pot that gets you high, Brennan said. “The cannabis now is much stronger, and that’s what people develop a dependence on and a withdrawal from.”

Cannabis withdrawal syndrome is more common in men and in people who use tobacco or other drugs along with pot, according to the new analysis by Dr Anees Bahji of Queen’s University in Ontario, Canada, and colleagues.

Heavy users are also more likely to experience withdrawal.

Feinstein pointed out that “there is no clear line that suggests how much use will cause withdrawal, and it will differ from person to person, but generally the data suggest that the likelihood of withdrawal increases with intensity of use and severity of addiction”.

Paul Armentano is deputy director of NORML, which advocates legalisation of marijuana. He said symptoms of withdrawal tend to be mild and short-lived, particularly when compared to those associated with other substances that are legal nationwide.

Worsening anxiety fro withdrawal

“By comparison, the profound physical withdrawal effects associated with tobacco are so severe that many subjects who strongly desire to quit end up reinitiating their use,” Armentano said. “In the case of alcohol, the abrupt ceasing of use in heavy users can be so severe that it can lead to death. Simply withdrawing from caffeine can lead to a number of adverse side effects, like rebound headaches.”

Brennan agreed. “Most symptoms go away in a few days,” he said. “Nearly all symptoms go away in a few weeks.”

But marijuana users need to be convinced that their symptoms are occurring because they’re quitting pot, or they’re liable to relapse, said Dr Scott Krakower, unit chief of psychiatry at Zucker Hillside Hospital in Glen Oaks, New York.

“People may feel that weed helps their anxiety level, but it may be more that you are developing worsening anxiety from marijuana withdrawal, rather than weed helping your anxiety level,” Krakower said. “It’s hard to explain to people that the symptoms they’re experiencing could be from them not using marijuana.”

Meanwhile, Brennan said folks experiencing symptoms of marijuana withdrawal should hang tough, and take over-the-counter remedies for physical ailments like nausea and headache.

“It does get better, and the symptoms do go away with time,” he said. “If they know there’s light at the end of the tunnel, maybe that will help motivate them to stick with it.”

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Work stress may increase your risk for ending up in the hospital with peripheral artery disease, a new study suggests.

Peripheral artery disease (PAD) occurs when cholesterol or other fatty substances accumulate in blood vessels away from the heart – usually in the legs – and restrict blood flow. Left untreated, PAD increases the risk of heart disease and stroke.

Previous studies have linked work stress to other types of artery-clogging disease, but few have specifically examined PAD.

This new study assessed the association between work stress and hospital treatment for PAD. The results were published on 28 April in the Journal of the American Heart Association.

Higher blood glucose levels

“Our findings suggest that work-related stress may be a risk factor for peripheral artery disease in a similar way as it is for heart disease and stroke,” lead study author Katriina Heikkilä said in a journal news release. She’s a senior researcher at the Karolinska Institute in Stockholm, Sweden.

Researchers analysed the health records of 139 000 men and women who took part in 11 studies conducted between 1985 and 2008 in Finland, Sweden, Denmark and the United Kingdom. Participants were ages 39–49 on average, and had no history of PAD when the studies began.

Over an average 13 years of follow-up, 0.2% to 1.8% of the participants were hospitalised for PAD. The risk was 1.4 times higher among those with work stress than among those without work stress, according to the study, though only an association was seen.

There is limited evidence linking job strain to heart disease, but stress is associated with increased inflammation and higher blood glucose levels. This could contribute to complications and worsening of PAD, according to the researchers.

PAD affects more than 200 million people worldwide, including more than 8.5 million in the United States. Symptoms include leg pain while walking.

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Middle-aged men and women who develop high blood pressure while performing even moderate exercise may be at higher risk for heart disease, a new study suggests.

“The way our blood pressure changes during and after exercise provides important information on whether we will develop disease in the future,” researcher Vanessa Xanthakis, assistant professor of medicine at Boston University School of Medicine, said in a university news release.

In the study, Xanthakis and her colleagues looked at the link between blood pressure levels, as well as the time needed for high blood pressure to recede back to normal, for nearly 2 000 people enrolled in a major ongoing US heart health study.

Participants averaged 58 years of age, about a quarter were obese, and about a third had hypertension at the beginning of the study.

Follow a healthy lifestyle

All of the participants were tested for changes in blood pressure while running at a “submaximal” level on a treadmill for three minutes at a stretch.

Their blood pressure readings were taken in the middle of the exercise bout, and then the rate at which blood pressure returned to normal (“recovered”) was recorded as they laid on their backs after the exercise.

Higher blood pressure during exercise was linked with a higher risk of developing hypertension over the 12 years of the study, the team found. As well, delays in blood pressure recovery after exercise were also associated with a higher risk of both heart disease and death during the study period, the researchers found.

Xanthakis believes that people should know their blood pressure numbers, speak to their doctor about changes in blood pressure during and after exercise, and follow a healthy lifestyle – including regular physical activity – to lower risk of heart disease later in life.

Dr Guy Mintz directs cardiovascular health at Northwell Health’s Sandra Atlas Bass Heart Hospital in Manhasset, New York. Reading over the new findings, he pointed out that in a typical cardiac stress test, “blood pressure is also monitored and reported as normal or as a hypertensive response to exercise – and that’s it. But now we see that an abnormal blood pressure response to exercise should be a wake-up call to the clinician.”

Sustained elevated pressure

This means that in a typical stress test, “useful data is left on the table that doctors can use to risk-stratify their middle-aged cardiovascular patient,” Mintz believes. “If we can identify this group of middle-aged patients early, we can intensify their cardiovascular risk reduction at a younger age.”

Another heart specialist agreed.

“As the arteries harden, they cannot relax after exercise during the recovery phase,” explained Dr Satjit Bhusri, a cardiologist at Lenox Hill Hospital in New York City. “This sustained elevated pressure during recovery is itself another independent marker of cardiovascular health,” he said, and “the quicker the return to normal, the healthier the cardiovascular system.”

The report was published online on 20 May in the Journal of the American Heart Association.

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