It was Buddha who said “your worst enemy cannot harm you as much as your own unguarded thoughts". Now science appears to have proved him right, after new researched showed that negative thoughts can be physiologically harmful, while positive thinking calms the heart rate and even boosts the immune system.

The findings suggest that taking time to think positive thoughts about oneself can make a significant health difference.

In a study carried out by academics at the universities of Exeter and Oxford, 135 healthy were divided into five groups and played a different set of audio instructions.

The team took physical measurements of heart rate and sweat response and asked participants to report how they were feeling.

Questions included how safe they felt, how likely they were to be kind to themselves and how connected they felt to others.

The two groups whose instructions encouraged them to be kind to themselves not only reported feeling more self-compassion and connection with others, but also showed a bodily response consistent with feelings of relaxation and safety.

Their heart rates dropped along with the variation in length of time between their heartbeats - a healthy sign of a heart that can respond flexibly to changing situations. They also showed lower sweat response.

Meanwhile, instructions that induced a critical inner voice led to an increased heart rate and a higher sweat response - consistent with feelings of threat and distress.

Lead researcher Dr Anke Karl, of the University of Exeter, said: "Previous research has found that self-compassion was related to higher levels of wellbeing and better mental health, but we didn't know why.

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"Our study is helping us understand the mechanism of how being kind to yourself when things go wrong could be beneficial in psychological treatments.

"By switching off our threat response, we boost our immune systems and give ourselves the best chance of healing.

"We hope future research can use our method to investigate this in people with mental health problems such as recurrent depression."

The recordings that encouraged self-compassion were a "compassionate body scan" in which people were guided to attend to bodily sensations with an attitude of interest and calmness; and a "self-focused loving kindness exercise" in which they directed kindness and soothing thoughts to a loved one and themselves.

The three other groups listened to recordings designed to induce a critical inner voice, put them into a "positive, but competitive and self-enhancing mode", or an emotionally neutral shopping scenario.

While people in both the self-compassion and positive-but-competitive groups reported greater self-compassion and decreased self-criticism, only the self-compassion groups showed the positive bodily response.

The study, Soothing Your Heart and Feeling Connected: A New Experimental Paradigm to Study the Benefits of Self-Compassion, is published in the journal Clinical Psychological Science.