In a worrying trend, teenagers in the US are increasingly getting less number of sleeping hours than they ideally should, finds a new study.

The study by researchers at Columbia found that female students, racial/ethnic minorities and students of lower socio-economic status are particularly affected.

“Declines in self-reported adolescent sleep across the last 20 years are concerning and suggest that there is potentially a significant public health concern that warrants health education and literacy approaches,” said lead author Katherine W. Keyes.

Inadequate sleep is associated with a wide range of health problems including mental health, academic problems, substance abuse and weight gain.

Students in the 8th, 10th and 12th grades of a nationally representative survey of more than 270,000 adolescents from 1991 to 2012 reported how often they get seven or more hours of sleep.

The largest decrease in the percentage getting seven hours of sleep per night was 15-year-olds. Among this age group, 72 percent reported regularly getting seven-plus hours of sleep per night in 1991.

By 2012, in the same age group, 63 percent of adolescents reported regularly receiving seven or more hours of sleep per night.

Seven hours per night is two hours less than the nine hours recommended by the National Sleep Foundation.

"Although the underlying reasons for the decrease in hours of sleep are unknown, there has been speculation that increased internet or social media use and pressures due to the heightened competitiveness of the college admissions process are adding to the sleep problem," Keyes noted.