Our physical body is the pinnacle of evolution and it has an inbuilt ability to completely heal itself. But it works only when our mind steps out of the way and allows the body to do its normal healing function. Our body keeps producing new cells to replace old cells all the time and in this way our entire body cells get replaced every two years. At any point of time our entire physical body is no older than two years. Why would the body be unhealthy when such an amazing process is happening naturally?
I can authoritatively confirm that regular practice of meditation results in complete freedom from pain and suffering. Even infections including very contagious ones like covid has no effect on such practioner. All chronic diseases are actually an outcome of modern urban lifestyle that keeps our mind continuously and restlessly engaged. Disease happens when the mind remains exhausted for a long time.
I have done extensive research and have written a book on this, which is under publication right now. People have no way to find out when the mind gets tired. With our physical body we know when it is tired and we pause physical activity and rest by sitting or lying or napping or sleeping or having a hot bath or massage. But with our mind, there is no metric to gauge its level of tiredness because mental tiredness shows up as restlessness, sadness, depression, anxiety, worry, indecisiveness, stress, or some such things and we end up treating it with more mental activity such as watching a movie or some other form of entertainment or distractions which always involves more mental activity and never rest. Meditation is the only way to rest the mind.
To answer your question, Yes, thinking directly impacts our health, it doesn’t matter if it is positive thinking or productive thinking or negative thinking or destructive thinking. Thinking is not just thoughts arising in the mind. It is our engagement with the arising thoughts that constitutes mental activity. Mental activity includes the monologues in our mind with ourselves, the dialogues we carry out mentally with an imaginary person, the voices of others in our mind telling us what not to do, memories of past events, worries about the future, planning, working, calculating, computing, watching something (videos) listening to something (such as podcasts), reading, studying, focusing, concentrating, paying attention, fantasising, imagining, dreaming, etc. We are habituated to this and so it seems to be happening effortlessly and automatically, although we are doing it. We don’t know how to stop it.
Even forcing the mind to not think or distracting the mind from thinking is still mental activity. We need to unlearn this habitual tendency by stepping out of the mind into body awareness and then into wholesome awareness of the present moment.
I have written several posts and answers on how to step out of the thinking mind and be quiet. Please browse through my Quora profile to read relevant articles that may be of further interest.