Dr. Kenji Takeuchi has made headlines recently for his research on the positive effects of laughter on the cognitive function of adults and senior citizens. But what few news sources have mentioned is that Dr. Takeuchi and his team of research scientists have been carrying out these very in-depth studies for several years. What’s even more interesting is how this topic came to be researched to begin with, especially considering that Dr. Takeuchi specializes in dental surgery and oral health, and not mental health. As it turns out, Dr. Takeuchi became interested in the link between laughter, smiling, and mental health after the Great East Japan Earthquake in March of 2011. After the earthquake many senior citizens lost their removable dentures. Since no previous studies had looked into the negative effects of denture loss post a natural disaster, Dr. Takeuchi and a team of 8 research scientists (four of which were dental surgeons) carried out an extensive study and published their findings in the Journal of Prosthodontics in September of 2014.

The study, which began almost immediately after the earthquake, was conducted through questionnaire surveys that measured various quality of life factors and took into account age, sex, economic status, dental helath history, psychological distress, and physical activity, among other things. The study found that participants who had lost their dentures were at significantly higher risk for eating difficulties, speech problems, embarrassment upon smiling, laughing, or showing their teeth, emotional distress, and problems related to social interaction. As a result of these findings, public health officials were persuaded to include dental care in their natural disaster response plans, but Dr. Takeuchi was keen on finding out how this information could be helpful in other areas, so he continued his research.

In May of 2021, 7 years after the original study and 10 years after the earthquake, Dr. Takeuchi and a team of 6 research scientists from various different fields, published another study. This new study was published in the Journal of Epidemiology run by the Japan Epidemiological Association and looked specifically into the connection between laughter and the onset of functional disability and mortality among seniors. This study had a much larger sample size than the first study, and focused on individuals aged 65 or older who could perform normal daily life activities without any assistance. The participants were classified into 4 groups according to how often they laughed: almost every day, 1-5 days per week, 1-3 days per month, and never or almost never. The researchers conducted 3-year follow-ups and noted participants who had developed functional disability. They found that participants who never laughed or almost never laughed were at a 1.42 times higher risk of developing cognitive functional disability than participants who laughed almost every day. They concluded that laughter may be an early predictor of functional disability later in life.

These findings seem to corroborate other studies linking repetitive negative thinking and Alzheimer’s. Indeed, Dr. Takeuchi’s research has already been cited in several other studies on the association between laughter and oral and mental health. It is important to note, however, that not every type of laughter will have the same positive effect on mental health. Laughter with loved ones, especially grandchildren, was found to be considerably more effective in lowering cognitive disability risk than simply laughing at a joke, for instance. This goes to show how important it is to maintain a rich and joyful social life.