For those who feel tired all the time, whether its in the office or at home, research has found obesity or depression could be to blame.

Research from Penn State College of Medicine has found obesity and depression are the leading causes of chronic drowsiness, the Juice Daily reports.

The study, as published in the SLEEP Journal, analysed 1300 people over 7.5 years and found those who were obese and depressed showed higher sleep disturbances and excessive levels of daytime sleepiness (EDS).

Dr Nicholas Fuller, an expert in obesity and metabolic disorders at University of Sydney's Charles Perkins Centre, told the Juice Daily that while this research is a well-supported study, using a novel new approach – a polysomnography test (a sleep study that uses brain wave technology) it isn't a new connection.

"We know already that people who are obese are sleepier during the day and that their night-time sleep is disturbed, compared to people of normal body weight."

Fuller believes what the study does do though, is highlight once more the lesser known health issues obesity can lead to, aside from a higher risk of type 2 diabetes, cardiovascular heart disease and some cancers.

“A lot less is known surrounding the day to day effects on quality of life, such as alertness, breathlessness, excessive sweating, joint pain, snoring and general lethargy," he said.

Experts also say depression often disturbs sleep and, conversely, disrupted sleep aggravates depression.