Caffeine

Caffeine absorption and half-life

It takes approximately 45 minutes for caffeine to reach 99% absorption in humans (Marks and Kelly, 1973; Bonati et al., 1982; Blanchard and Sawers, 1983a,b; Arnaud, 1993). For doses lower than 10 mg/kg (4.54 mg per lb; or 590 mg for a 130 lb person), caffeine half-lives (the time for half of the chemical to leave your body) range from 2.5 to 4.5 h in humans (Arnaud, 1987). Caffeine half-life is approximately doubled in women taking oral contraceptives (Patwardhan et al., 1980) . That is, for a woman taking oral contraceptives, the half life of caffeine is an average of 5 to 8 hours.

Effect on Sleep

Caffeine has been demonstrated to delay the onset of sleep (see Eichler, 1976; Snel, 1993). Effects on sleep are quite variable. Levy and Zylber-Katz (1983) suggested that individuals with heightened sensitivity to caffeine may be metabolizing the caffeine slower.

A caffeine dose equivalent to one cup of coffee taken at bedtime increases the time it takes to fall asleep and decreases the reported quality of sleep, in addition to causing changes in the EEG pattern during sleep, especially in the non-REM deep sleep (Landolt et al., 1995a).

Withdrawal Symptoms

Humans can experience a variety of withdrawal symptoms. These include weariness, apathy, weakness and drowsiness, headaches, anxiety, decreased motor behavior, increased heart rate, and increased muscle tension and, occasionally, tremor, nausea, vomiting, and flu-like feelings (Griffiths et al., 1990; Silverman et al., 1992; Nehlig and Debry, 1994; Höfer and Bättig, 1994a,b; Strain et al., 1994; Griffiths and Mumford, 1995; Schuh and Griffiths, 1997).

Withdrawal symptoms typically appear approximately 12 to 24 h from last caffeine consumption and reach a peak after 20 to 48 h.

However, some people experience withdrawal symptoms after 3 to 6 h, and such symptoms can last for 1 week (Barone and Roberts, 1984; James, 1991; Nehlig and Debry, 1994; Phillips-Bute and Lane, 1998). Thus, even a short abstinence, equivalent to missing the morning cup of coffee, can lead to significant unpleasant effects (Phillips-Bute and Lane, 1998).

Furthermore, in a group that alternated between 1 day of caffeine consumption and 2 caffeine-free days, the complaints decreased from the first period of abstinence to the next and vanished almost completely by the third one, demonstrating that more than 1 day of previous caffeine exposure is needed to induce withdrawal symptoms (Höfer and Bättig, 1994a,b).

How to cut back on caffeine

If you want to cut back on caffeine, I would recommend cutting by approximately 0.5-1 "cups" (the 8 oz size) of coffee per day. For example, switching from a large to a medium coffee.

Additional Reading

Caffeine FAQ.

Caffeine Question: Should You Decaffeinate Your Diet? (Mayo Foundation for Medical Education and Research) 

References:

1. Fredholm BB, Bättig K, Holmén J, Nehlig A, Zvartau EE. Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacol Rev. 1999 Mar;51(1):83-133.

2. See additional reference info at 1.