Faith-based groups are an underused health resource that can be the key to achieve adequate health care for all, expediting response to some of the biggest global health challenges of the 21st century, a new study says.

Faith-based organisations are crucial in achieving the promise of universal health coverage, especially for poor and marginalised groups, according to the new three-part series on faith-based health care published in the prestigious journal The Lancet.

The researchers argue that building on the extensive experience, strengths and capacities of faith-based organisations offers a unique opportunity to improve health outcomes across the world.

Because of their broad reach and influence, faith-based groups have for centuries played critical roles in delivering education, health and social services.

"Not every community has health services but most have some type of faith-based group," said professor Edward Mills from Global Evaluative Sciences in Vancouver, Canada.

"Religious groups are major players in the delivery of healthcare, particularly in hard-to-reach and rural areas that are not adequately served by government. Yet, the general medical community knows very little about them," Mills added.

The available evidence indicates that faith-based health providers play an important part in meeting public health needs such as immunisation, anti-malarial campaigns, preventing mother and child deaths and HIV services, especially in fragile health systems.

For example, during the Ebola outbreak in west Africa, faith groups were key mediators of community education, especially safe burial, while providing vital medical services and support.

"With more support from governments, donors and international faith networks, these movements can rapidly scale up to reach millions of people with critical health issues," the authors wrote.

Faith-based organisations often represent the only health infrastructure in a region and have strong cultural ties to the communities.

"It is time for the general medical community to recognise the magnitude of services offered and partner or support to provide long-standing improvements in health," they said.