Study under review: Effects of caffeine on the human circadian clock in vivo and in vitro
Caffeine has been a component of the human diet for centuries, primarily through the consumption of coffee and tea. Culturally, coffee and tea are two of the main beverages that tie together many human interactions. Chemically, caffeine is well-known for being an adenosine receptor antagonist that blocks the action of adenosine. Because adenosine mediates the perception of drowsiness, caffeine consumption results in alertness.
A circadian rhythm is essentially an organism's daily internal clock. It is not restricted to humans and exists in most living things, even bacteria. For us, the circadian clock follows a roughly 24-hour cycle, responding primarily to light and darkness in our environment, and acting to regulate countless bodily functions. One of the most important hormones in this context is melatonin, which is released by the pineal gland in the brain and is involved with sleepiness and sleep regulation.
Melatonin is secreted in response to darkness to help prepare the body for sleep. It is well-established that exposure to bright light suppresses melatonin production. However, the ability of a stimulus to interfere with normal circadian function depends on the time of day. A pulse of blue light before bed will indeed suppress melatonin production and delay sleep, but that same pulse of light at noon will have no effect because melatonin production is low at noon anyway.
However, one recent population-based study of adults estimated that 90% of individuals consume caffeine in the afternoon (12:00-6:00 pm) and 68.5% of people consume caffeine in the evening (6:00 pm - 12:00 am). Similarly, 37% of high schoolers who consume caffeine report not using it until after 5:00 pm. Dose-response studies in humans and animals demonstrate that increasing doses of caffeine administered at or near bedtime are associated with significant sleep disturbance. Thus, the current study attempted to test whether nighttime caffeine consumption would delay the normal circadian rhythm of melatonin production, and evaluated the cellular mediators of any potential effect.
Research has backed the commonly seen experience of caffeine late in the day disrupting sleep and hence circadian rhythms. The specific mechanisms for this, as well as impact on the sleep hormone melatonin, are not fully understood though.
Other Articles in Issue #13 (November 2015)
What are you feeding your bacteria?
While probiotics get most of the press, prebiotics arguably have more potential for altering one’s microbiome. This study looks at a promising type of prebiotic supplement to see if it might impact appetite and inflammation.
Breakfast: A disempowering nutritional dogma
By Martin MacDonald, Msc
Return of the globule: milk fat strikes back
Milk fat is structurally different than most other fats, and the milk fat globule membrane has been looked at previously (twice in Study Deep Dives, in fact) for its impact on chronic disease. But could it also impact response to exercise?
Studies have shown that supplement buyers generally trust the supplements they buy. That might not be the safest assumption, as dietary supplements that are presumed helpful or neutral may sometimes cause serious side effects, as quantified by this study.
Probiotics and the propensity for portliness
When you eat a meal, your gut bacteria also eats a meal. And gut bacteria are increasingly looked at for their influence on chronic disease. This study looks at the effect of a specific probiotic blend on weight gain.
Money, time, and the science that suits us
By David Katz, MD, MPH
Human eating patterns ... there’s an app for that
Eating throughout the day has become quite normal, given the ubiquitous availability of snack foods. Partly due to this, diet research has been plagued by inaccurate self-reports. This study used an app to get around that issue.
Does marijuana actually boost creativity?
Ancedotally, weed has been claimed as a creativity booster for decades. With THC having an effect on dopamine, a plausible mechanism exists. This randomized trial puts marijuana to the test.
Diet and autism: no gluten, no casein, no difference?
Gluten and casein are two food components often linked with autism spectrum disorder symptoms. Hence the prevalance of wheat and dairy free diets. But will they work in a rigorously controlled trial?