The United States has become the 21st country to have legalized same-sex marriage nationwide. The history was made on Friday and the US is now in line with its neighbors Mexico and Canada.

Celebrations are on in the US and a health-linked LGBTQ study has also been announced. Two San Francisco doctors have started the study which involves the use of the technology developed by Apple Inc. The app called PRIDE has made it possible to conduct the ambitious study of the LGBT health.

Patients and researchers will be connected to each other with the help of the cloud used by ResearchKit, the newly-launched medical research framework tool of Apple.

ResearchKit has got support of many large health groups, but its effectiveness is still unclear. The launch of ResearchKit took place in April.

Doctors Mitchell Lunn and Juno Obedin-Maliver created the PRIDE app. The duo works at the University of California in San Francisco.

According to Lunn, focus on listening is the priority of the app in the first year, and a more rigorous, in-depth study will be launched next year to include the contributions of the community.

The PRIDE app powered by ResearchKit respects the privacy of the participant, who requires to submit information like race, ethnicity, age and location.

"Ideally we want to get tens of hundreds of members and comply with individuals for many years, one thing like 30 years. The aim is to determine how being a sexual or gender minority influences bodily or psychological health", said Lunn.

The National Public Radio has revealed in a report that one in three people from the LGBT community is a smoker.