Daylight Saving Time (United States) began Sunday, March 11, 2012, 2:00am, and ended Sunday, November 4, 2012, 2:00am. Daylight saving time (DST) — also summer time in several countries in British English, and European official terminology — is the practice of advancing clocks so that evenings have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn.
Daylight saving time – DST has mixed effects on health. In societies with fixed work schedules it provides more afternoon sunlight for outdoor exercise. It alters sunlight exposure; whether this is beneficial depends on one’s location and daily schedule, as sunlight triggers vitamin D synthesis in the skin, but overexposure can lead to skin cancer.
Sunlight strongly influences seasonal affective disorder, both the summer version and the winter version; the use of DST, with unnatural late sunsets, for two-thirds of the year has a greater impact on summer SAD sufferers than normal standard time does on winter SAD sufferers in winter.
DST may help in depression by causing individuals to rise earlier, but some argue the reverse.
The Retinitis Pigmentosa Foundation Fighting Blindness, chaired by blind sports magnate Gordon Gund, successfully lobbied in 1985 and 2005 for US DST extensions, but DST can hurt eyes, eye problems and night blindness sufferers.
Clock shifts disrupt sleep and reduce its efficiency. Effects on seasonal adaptation of the circadian rhythm can be severe and last for weeks.
A 2008 Swedish study found that heart attacks were significantly more common the first three weekdays after the spring transition, and significantly less common the first weekday after the autumn transition.
The government of Kazakhstan cited health complications due to clock shifts as a reason for abolishing DST in 2005.