With daylight saving time coming to an end, millions of Americans will be setting their clocks back one hour before bed on Saturday. 

It will be lighter earlier in the morning going forward, and grow darker earlier in the evening. 

WHAT IS DAYLIGHT SAVING TIME AND WHY DOES MOST OF ARIZONA NOT OBSERVE IT?

Hawaii, most of Arizona, American Samoa, Guam, Puerto Rico and the U.S. Virgin Islands do not observe the time change

However, while residents of the other states gain an hour of sleep, many still question the health effects of daylight saving time. 

According to Mayo Clinic, the human brain has a circadian, or biological clock, that runs on a 24-hour cycle. 

Scott Gow assembles a clock dial for a four-dial street clock headed to the Lincoln Haymarket Historic District in Nebraska at the Electric Time Company in Medfield, Massachusetts November 1, 2013.   (REUTERS/Brian Snyder)

Disruptions due to daylight saving time – mainly in the spring – can impact a person's ability to focus during the day. 

Sleep Foundation notes that some people experience insomnia due to springtime changes, that circadian misalignment can contribute to "sleep debt" and that cardiovascular health can also be impacted. 

DAYLIGHT SAVING TIME: WHEN AND WHY WE 'FALL BACK'

While sleep disturbances are less likely during the transition from daylight saving time to standard time in November, fewer daylight hours can also lead to traffic accidents, as well as mental health issues.

Time and Date says that setting the clocks back can trigger bipolar disorder, winter blues and seasonal affective disorder (SAD). 

SAD is a type of depression related to seasonal changes that typically occurs during the fall and winter months. 

The mood disorder is more common in women and younger people, and with those who live in places with long winter nights, experts say. 

Symptoms include feelings of hopelessness, reduced energy and focus, social withdrawal, increased sleep, loss of interest in work or other activities, sluggish movements, increased appetite with weight gain, and unhappiness and irritability.

The National Institute of Mental Health (NIMH) says symptoms can last four to five months.

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Treatments for SAD include light therapy using 10,000 lux light boxes, medications, vitamin D and psychotherapy. 

The Cleveland Clinc also recommends that people who suffer from the disorder eat a well-balanced diet, exercise, see friends and spend more time outdoors.

Standard time begins at 2 a.m. local time on Sunday

The Associated Press contributed to this report.