Sleep, Circadian Rhythms and Caffeine

Ever wondered what it is that regulates our sleep patterns? What is all that tea and coffee is doing to us? Why do so many people have so much trouble getting to sleep? (There are some great hubs about sleep disturbances and I will include links to them below.) As many people already know, the side effects of too much coffee and tea can be debilitating and even harmful to health and well being. But is the problem about how much we consume or the pattern of consumption? Should we be drinking small amounts of caffeine throughout the day or should we stick with the 'big jolt in the morning' model?

Caffeine is one of the three most widely used drugs in the world (the others are nicotine and alcohol). The human body reacts almost instantly to caffeine. The speed and intensity of the reaction to caffeine depends on a person's weight and other physiological factors and is a very individual thing. Caffeine stays in your blood for around 12 hours after ingestion. It is a mood affecting drug as well as having physical side effects. Caffeine:

• makes your heart rate go up;
• stimulates your central nervous system (CNS);
• affects your breathing;
• elevates mood;
• decreases fatigue;
• causes your stomach to produce more acid;
• can result in in increased urination (diuretic affect);
• can alter blood sugar levels;
• increases blood circulation;
• elevates blood pressure;
• elevates the levels of fatty acids in your blood;
• can create restlessness and irritability;
• can result in difficulty concentrating;
• causes caffeine dependence;
• can result in miscarriages and birth difficulties (with heavy usage);
• can cause an increase in breast tenderness; and
• can result in insomnia.

In the worst case scenario caffeine can contribute to heart rhythm disorders, prolonged or chronic depression and panic attacks. It is no surprise that heavy caffeine usage has been liked to high blood pressure, oesteoperosis, insomnia, heartburn, ulcers and even infertility.

On the positive side, there is some evidence that caffeine can also result in a reduced risk of developing heart disease.

The number one offender is coffee with anywhere from 60-500 milligrams of caffeine per cup depending on whether it is instant, espresso, percolated or filter coffee. Tea has approximately 35-40 milligrams. Other sources of caffeine include:

• Chocolate;
• Soft drinks;
• Energy drinks;
• Some vitamin compounds; and
• Some medications.

Your circadian rhythm is governed by the physical, behavioural and mental changes that occur in relation to light and darkness over an approximate 24 hour period. The circadian rhythm is driven by the biological clock which is in turn driven by about 20,000 nerve cells in the hypothalamus in the brain. Circadian rhythms can cause alterations in sleep-wake cycles, temperature and hormone release among other things.

The relationship between circadian rhythms and sleep-wake cycles is regulated by the production of the hormone melatonin. The hypothalamus is located near the optic nerve and the amount of light will in turn stimulate or decrease melatonin production which influences how drowsy a person is.

We all know that caffeine keeps you awake. However, scientists still do not know the exact answer to the question of why this is so. While they know that caffeine works by interfering with two interacting systems (the homeostatic system and the circadian clock) that regulate the sleep-wake cycle, they do not know exactly how it achieves this. They think that caffeine blocks the actions of a messenger chemical - adenosine (which sends messages to the homeostatic system to induce sleep). Adenosine is a powerful natural sleep inducing chemical. It seems that caffeine has a more powerful effect on the homeostatic system than on the circadian clock.

If caffeine does block adenosine, the logical inference is that caffeine can allow people to take control of their sleep patterns, defying their circadian clocks. This is a good thing for shift-workers and global travellers but it seems that few people know how to do this effectively.

Scientists have done surveys on shift-workers that show that it is far better to have small amounts of caffeine throughout the day than a big hit in the morning. The test subjects who took low dose frequent caffeine did better on cognitive testing, although they apparently did continue to feel sleepy.

I know that I feel as though I need that caffeine hit in the morning to get me going. I also know that come early afternoon I am flagging and the screen gets a bit hazy. I might take their advice and drink a third of a cup frequently instead of about three cups before 10am and none after then. 

Much of this information was obtained from the following:

• Harvard Medical School (2004, May 12). Small, Frequent Doses Of Caffeine Best Strategy For Staying Awake, According To New Study.
• National Geographic Magazine, (January 2005). Caffeine: it's the worlds most popular psychoactive drug.
• National Institute of General Medical Sciences (July 2008) Circadian Rhythms Fact Sheet.