Cardiovascular system--More strokes and heart attacks occur in the morning than at any other time of day. This makes some people wonder if morning exercise is safe. But experts contend morning changes in your body--not exercise-- may be responsible for cardiovascular problems. Blood clots most rapidly at about 8 a.m.
Blood pressure also rises in the morning and stays elevated until late afternoon. Then it drops off and hits its lowest point during the night.
These changes occur independently of physical activity. Exercise at any time of the day is beneficial.
On the other hand, if you're training for athletic competition, you may have reason to schedule that event later in the day. Athletes seem to perform best in the late afternoon, when strength, body temperature and flexibility peak.
Pain tolerance--Athletes who compete late in the day may perform better because they can "gain" without as much "pain." Pain tolerance is highest in the afternoon. One study shows tooth pain is lowest in the late afternoon, a consideration when you schedule your next dental appointment.
Medication--Scientists are looking at how circadian rhythms affect the way your body uses medications. One finding is that less anesthesia is needed to cause analgesia or drowsiness when administered in the afternoon.
Experiments with cancer medications are trying to find the time of day when the drugs are the most helpful with the fewest side effects.
Sex --The majority of sexual encounters took place at bedtime (11 pm to 1 am). The most common explanations for this temporal pattern is the biological clock has a time set for sexual arousal.
Heart attacks--The chances of suffering heart problems are not equal throughout the day. Heart attacks occur more often around 10 o'clock in the morning than any other time, a peak that previously was attributed to daily behavior patterns getting underway
Stay on schedule
Changes in daily habits such as a short night's sleep can disrupt your circadian rhythms. You may be able to stay "in sync" by keeping a consistent daily schedule.
Blind:
Most totally blind people have circadian rhythms that are "free-running" (i.e., that are not synchronized to environmental time cues and that oscillate on a cycle slightly longer than 24 hours). This condition causes recurrent insomnia and daytime sleepiness when the rhythms drift out of phase with the normal 24-hour cycle.10-mg dose of melatonin was given daily one hour before bedtime will achive a normal ryththm.. The dose was then reduced to 0.5 mg per day over a period of three months; the entrainment persisted, even at the lowest dose.
Smith-Magenis syndrome.
Age progression of female subjects with SMS. Typical SMS infant phenotype with 'tented' upper lip and depressed nasal bridge at birth (a), at age 4 months (b), and with hand-clasping behavior at age 1 year (c) is shown. A white patch on the dorsum of left forearm due to skin picking is illustrated in a toddler (also hand clasping) at age 2 years (d). The same individual at ages 13 years (e) and 20 years (f), and photos at 21 years of age illustrating open wounds and scarring on forearms from skin picking (g), brachydactyly and nail-yanking lesions on hands (h), and feet with brachydactyly and nails damaged from nail yanking (i).
These patients present major sleep disturbances ascribed to a phase shift of their circadian rhythm of melatonin with a paradoxical diurnal secretion of the hormone. Treatment with morning beta-blockers and evening melatonin reinstated a normally timed melatonin circadian rhythm, improved daytime behavior and restored normal sleep habits, resulting in a greatly improved quality of life for both SMS patients and their family. SMS is the demonstration of biological basis for sleep disorder in a genetic disease.Mol Cell Endocrinol. 2006 May 22De Leersnyder H,
