The first combed 148 studies, involving more than 3,00,000 participants, and found that deep social ties were associated with a 50% reduced risk of early death.
In May, a study carried out for the Jo Cox commission on loneliness found that nearly three-quarters of older people in the United Kingdom are lonely and more than half of those have never spoken to anyone about how they feel.
These trends suggest that Americans are becoming less socially connected and experiencing more loneliness, said the researchers.
An American Association of Retired Persons' (AARP) study by the name "Loneliness Study" estimates almost 42.6 million adults in United States, who are above 45 years old, as suffering from chronic loneliness.
Loneliness and social isolation are a greater public health burden than obesity, scientists have argued. One involved 148 studies, representing more than 300,000 participants across the USA, and the second involved 70 studies representing more than 3.4 million individuals primarily from North America but also from Europe, Asia, and Australia.
For the study, Professor Holt-Lunstad and colleagues sought to determine how loneliness and social isolation influence the risk of early death by conducting two "meta-analyses" of previous studies.
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In her second analysis, she looked at the role that loneliness, social isolation, and living alone played in a person's lifespan. National census shows that a quarter of these lonely people are living by themselves, half of the population are single basing from the last national population survey.
She highlighted social connection as a "fundamental human need", and mourned the fact that an increasing part of USA population now experiences isolation on the regular. Further, the latest census data shows that over 25% of the country's population lives alone, that more than half of the total population is unmarried, and that marriage rates and the number of kids per household have dropped.
With the above findings showing how loneliness could potentially be more unsafe than obesity in terms of one's chances of premature death, Holt-Lunstad stressed that people in general should be armed with the right tools to prevent loneliness from becoming a problem later in life.
The researchers said greater priority be placed on social skills training for children in schools while doctors should be encouraged to include social connectedness in medical screening, she said.
Additionally, people should be preparing for retirement socially as well as financially, for example, choosing to live somewhere with access to recreation centers and community gardens.
Holt-Lunstnd also said that by the increase of the aging population, the effect on public health is expected to rise.