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Bioclock

How your body's clock affects your memory and thinking

Low-salt diet doesn't help blood pressure if body clock broken

Lower salt generally lowers blood pressure, but it turns out this may not apply in all instances. A mouse study suggests that a low-salt diet can increase the risk of hypertension if you have a disrupted circadian rhythm. Sleep disorders, shift work, disease, and aging are all potential signs of or triggers for circadian dysfunction.

A 24-hour blood pressure check may reveal that blood pressure is not falling, as it should, during the night. Nondipping blood pressure is estimated as high as 53% in patients being treated for hypertension. It may be that, for those with a disrupted circadian rhythm, the timing of antihypertensive medication should be different.

http://www.eurekalert.org/pub_releases/2016-02/mcog-wab020116.php

Pati, P., Fulton, D. J. R., Bagi, Z., Chen, F., Wang, Y., Kitchens, J., … Rudic, R. D. (2016). Low-Salt Diet and Circadian Dysfunction Synergize to Induce Angiotensin II–Dependent Hypertension in Mice. Hypertension, 67(3), 661–668. http://doi.org/10.1161/HYPERTENSIONAHA.115.06194

Immune system has seasonal cycle

A study has revealed that the immune system has a seasonal cycle, in which its activity is boosted during the winter and relaxes during the summer. While the winter increase in immune defences presumably helps us stave off infections, it also raises the risk of harmful inflammation, effectively lowering the threshold for heart attacks, stroke, diabetes and even some psychiatric conditions. This may explain why deaths from conditions ranging from heart attacks to diabetes and schizophrenia increase in winter.

The study used blood samples from more than 16,000 people living in both the northern and southern hemisphere

http://www.theguardian.com/science/2015/may/12/winter-immune-boost-may-actually-cause-deaths-study-suggests

Dopico, X. C., Evangelou, M., Ferreira, R. C., Guo, H., Pekalski, M. L., Smyth, D. J., … Todd, J. A. (2015). Widespread seasonal gene expression reveals annual differences in human immunity and physiology. Nature Communications, 6, 7000. http://doi.org/10.1038/ncomms8000

Offices with no windows linked to lousy sleep

A study involving 49 office workers, of whom 27 worked in windowless workplaces and 22 in workplaces with windows, has found that those exposed to natural light slept better, and were also more active.

Employees with windows in the workplace received 173% more white light exposure during work hours and slept an average of 46 minutes more each night.

Workers without windows had lower scores on quality of life measures related to physical problems and vitality, as well as poorer outcomes on measures of overall sleep quality and sleep disturbances.

http://www.futurity.org/windows-workers-sleep-health-745022/

Boubekri M, Cheung IN, Reid KJ, Wang CH, Zee PC. Impact of windows and daylight exposure on overall health and sleep quality of office workers: a case-control pilot study. J Clin Sleep Med 2014;10(6):603-611.

Shift workers at higher risk of diabetes

A review of 12 studies involving more than 225,000 people, of whom almost 15,000 had diabetes, has found that shift work carries a 9% higher risk of type 2 diabetes, especially in men and those with rotating shift patterns. Men, in fact, had a 37% greater risk of developing diabetes if they did shift work, while those who did rotating shifts had a 42% higher risk than those who worked a fixed shift pattern.

http://www.theguardian.com/society/2014/jul/25/shift-workers-higher-risk-type-2-diabetes-study

Gan, Y., Yang, C., Tong, X., Sun, H., Cong, Y., Yin, X., … Lu, Z. (2015). Shift work and diabetes mellitus: a meta-analysis of observational studies. Occupational and Environmental Medicine, 72(1), 72–78. http://doi.org/10.1136/oemed-2014-102150

How hard your brain works depends on the season

A sleep study involving 28 participants had them follow a controlled sleep/wake schedule for three weeks before staying in a sleep laboratory for 4.5 days, during which time they experienced a cycle of sleep deprivation and recovery in the absence of seasonal cues such as natural light, time information and social interaction. The same participants went through this entire procedure several times over some 18 months. Brain activity was assessed while participants undertook an n-back working memory task, and a task that tested sustained attention.

Broken bioclock linked to Alzheimer's-type brain damage

Submitted by Fiona McPherson on

A study involving mice lacking a master clock gene called Bmal1 has found that as the mice aged, their brains showed patterns of damage similar to those seen in Alzheimer's disease and other neurodegenerative disorders. Many of the injuries seemed to be caused by free radicals. Several key antioxidant enzymes, which usually neutralize and help clear free radicals from the brain, have been found to peak in the middle of the day in healthy mice, but not in these mice lacking Bmal1.

Why sleep is disrupted in Alzheimer's disease

Submitted by Fiona McPherson on

A study involving genetically engineered fruit flies adds to our understanding of why sleep and bioclock disruptions are common in those with Alzheimer's disease. People with Alzheimer's often have poor biological rhythms — periods of sleep become shorter and more fragmented, resulting in periods of wakefulness at night and snoozing during the day. It has been thought that Alzheimer’s destroys the biological clock, but this new study indicates that the clock is still working — however, it’s being ignored by other parts of the brain.

Meal-time affects cholesterol in liver

Submitted by Fiona McPherson on

A mouse study suggests that merely changing meal times could have a significant effect on the levels of triglycerides in the liver. Levels of triglycerides followed a circadian rhythm, with levels peaking about eight hours after sunrise (note that mice are nocturnal). Mice generally eat 20% of their food during the day, and 80% at night. Mice lacking a functional body clock eat constantly during the day. When normal mice were given the same amount of food, but had to eat it only at night, there was a quick and dramatic 50% decrease in overall liver TAG levels.

Circadian rhythm

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See also:

Time of day effects in immediate and delayed memory

Sleep loss and temporal memory

Circadian clock may be critical for remembering what you learn

We know circadian rhythm affects learning and memory in that we find it easier to learn at certain times of day than others, but now a study involving Siberian hamsters has revealed that having a functioning circadian system is in itself critical to being able to remember. The finding has implications for disorders such as Down syndrome and Alzheimer's disease. The critical factor appears to be the amount of the neurotransmitter GABA, which acts to inhibit brain activity. The circadian clock controls the daily cycle of sleep and wakefulness by inhibiting different parts of the brain by releasing GABA. It seems that if it’s not working right, if the hippocampus is overly inhibited by too much GABA, then the circuits responsible for memory storage don't function properly. The effect could be fixed by giving a GABA antagonist, which blocks GABA from binding to synapses. Recent mouse studies have also demonstrated that mice with symptoms of Down syndrome and Alzheimer's also show improved learning and memory when given the same GABA antagonist. The findings may also have implications for general age-related cognitive decline, because age brings about a degradation in the circadian system. It’s also worth noting that the hamsters' circadian systems were put out of commission by manipulating the hamsters' exposure to light, in a technique that was compared to "sending them west three time zones." The effect was independent of sleep duration.

Ruby, N.F. et al 2008. Hippocampal-dependent learning requires a functional circadian system. Proceedings of the National Academy of Sciences, 105 (40), 15593-15598.

http://www.eurekalert.org/pub_releases/2008-10/su-ccm100808.php

Morningness a predictor of better grades in college

A survey of 824 undergraduate students has found that those who were evening types had lower average grades than those who were morning types.

The finding was presented at SLEEP 2008, the 22nd Annual Meeting of the Associated Professional Sleep Societies (APSS).

http://www.eurekalert.org/pub_releases/2008-06/aaos-map050708.php

Mice brains shrink during winter, impairing spatial memory

A study involving adult male white-footed mice may help us understand seasonal dysfunctions such as seasonal affective disorder. The study found that those mice kept in artificial light conditions mimicking winter (8 hours of light per day) had impaired spatial memory compared to mice kept in “summer” conditions (16 hours per day). They also had, on average, smaller brains, with a proportionally smaller hippocampus, as well as changes in dendritic spine density in that region. Other types of memory did not appear to be affected.

Pyter, L.M., Reader, B,F. & Nelson, R.J. 2005. Short Photoperiods Impair Spatial Learning and Alter Hippocampal Dendritic Morphology in Adult Male White-Footed Mice (Peromyscus leucopus). Journal of Neuroscience, 25, 4521-4526.

http://www.eurekalert.org/pub_releases/2005-05/osu-mbs051205.php

Repeated, frequent episodes of jet lag without sufficient recovery time may reduce cognitive function

A study of 20 flight attendants suggests that people who undergo repeated, frequent episodes of jet lag without sufficient recovery time between trips may develop actual tissue changes in the brain in an area that's involved in spatial orientation and related aspects of cognitive function. The extent to which this is due to sleep deprivation rather than time shifts per se is unknown. These findings may also be relevant to shift workers, medical trainees and others who work long hours.

Cho, K. 2001. Chronic 'jet lag' produces temporal lobe atrophy and spatial cognitive deficits. Nature Neuroscience, 4 (6), 567-568.

Chronic jet lag has long-lasting effects on cognition

Twice a week for four weeks, female hamsters were subjected to six-hour time shifts equivalent to a New York-to-Paris airplane flight. Cognitive tests taken during the last two weeks of jet lag and a month after recovery from it revealed difficulty learning simple tasks that control hamsters achieved easily. Furthermore, the jet-lagged hamsters had only half the number of new neurons in the hippocampus that the control hamsters had.

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