Denmark has overtaken Switzerland as the world's happiest place, according to a report that urged nations regardless of wealth to tackle inequality and protect the environment.

The report, prepared by the Sustainable Development Solutions Network (SDSN) and the Earth Institute at Columbia University, showed Syria, Afghanistan and eight sub-Saharan countries as the 10 least happy places on earth to live.

The top 10 this year were Denmark, Switzerland, Iceland, Norway, Finland, Canada, Netherlands, New Zealand, Australia, and Sweden. Denmark was in third place last year, behind Switzerland and Iceland.

The bottom 10 were Madagascar, Tanzania, Liberia, Guinea, Rwanda, Benin, Afghanistan, Togo, Syria and Burundi.

The United States came in at 13, Ireland was 19th on the list, the United Kingdom was 23rd, France at 32, and Italy at 50.

"There is a very strong message for my country, the United States, which is very rich, has gotten a lot richer over the last 50 years, but has gotten no happier," said Professor Jeffrey Sachs, head of the SDSN and special advisor to UN Secretary General Ban Ki-moon.

While the differences between countries where people are happy and those where they are not could be scientifically measured, "we can understand why and do something about it," Mr Sachs, one of the report's authors, told Reuters in an interview in Rome.

"The message for the United States is clear. For a society that just chases money, we are chasing the wrong things. Our social fabric is deteriorating, social trust is deteriorating, faith in government is deteriorating," he said.

Aiming to "survey the scientific underpinnings of measuring and understanding subjective well-being," the report, now in its fourth edition, ranks 157 countries by happiness levels using factors such as per capita gross domestic product (GDP) and healthy years of life expectancy.

It also rates "having someone to count on in times of trouble" and freedom from corruption in government and business.

"When countries single-mindedly pursue individual objectives, such as economic development to the neglect of social and environmental objectives, the results can be highly adverse for human wellbeing, even dangerous for survival," it said.

"Many countries in recent years have achieved economic growth at the cost of sharply rising inequality, entrenched social exclusion, and grave damage to the natural environment."

The first report was issued in 2012 to support a UN meeting on happiness and well-being.

Five countries - Bhutan, Ecuador, Scotland, United Arab Emirates and Venezuela - now have appointed Ministers of Happiness charged with promoting it as a goal of public policy.

The 2016 survey showed that three countries in particular, Ireland, Iceland and Japan, were able to maintain their happiness levels despite external shocks such as the post-2007 economic crisis and the 2011 earthquake because of social support and solidarity.

Mr Sachs pointed to Costa Rica, which came in 14th and ahead of many wealthier countries, as an example of a healthy, happy society although it is not an economic powerhouse.