Heena Gupta, M. Optom

Paediatric Optometrist, Tamojyoti Netralaya, Gurgaon, India

Caffeine is a methylxanthine and can be derived from sources such as kola nuts, coffee beans, and cocoa. It is contained in most of the things we eat and drink, such as chocolates, cold drinks, coffee, tea, cocoa, and many other beverages. As stated by Goodman and Gilman, ⁽¹⁾  the different sources of caffeine vary in their caffeine content.

For example:

• 1 cup of coffee (150 ml): 67-175 mg of caffeine
• 1 cup of tea (150 ml): 50 mg of caffeine
• 1 mg of theophylline; 1 cup of cocoa (150ml): 5mg of caffeine
• 250 mg of theobromine; 12 oz/36 cl bottle of cola drink: 40-50 mg of caffeine
• 1 bar of chocolate: 25 mg of caffeine per 30 g.

The effects of caffeine on the body are dose related. The effect on the body systems could be subtle at low doses, overt at high doses, and consumers are at risk of becoming victims of caffeine addiction.⁽²⁾ It has effects such as stimulation of mental activity, an increase in blood pressure and heart rate, smooth muscle relaxation (bronchodilator), diuresis, sleep disruption, and improvement in physical performance. Caffeine is of great therapeutic importance, being used in the treatment of neonatal apnea and dyspnea, and it serves as an adjuvant in several pharmaceutical preparations.⁽³⁾

Caffeine affects the nervous system and therefore the production of aqueous tears by the lacrimal gland, which depends on the nervous system. It has anticholinergic effects by its antagonism of adenosine receptors, and thus has a potential effect on the lacrimal gland. The reduction of glandular secretion induced by caffeine is one of its many anticholinergic effects.⁽⁴⁾ Among agents that frequently reduce tear secretion are anticholinergics, antihistamines, and antianxiety drugs.⁽⁵⁾

The effects of caffeine on tear production are due to the time of onset of caffeine in the body. The absorption of caffeine from the gastrointestinal tract is reported to be rapid and reaches the bloodstream.⁽⁶⁾ The peak effect of coffee occurs after 60 minutes, which could be explained by the fact that caffeine attains maximum plasma concentration within 60 minutes.⁽⁷⁾ This effect of caffeine on tear production is believed to result in the stimulation of the release of noradrenaline from both adrenal glands and sympathetic nerves, thereby producing an increase in sympathetic activation.⁽⁸⁾ Sympathetic stimulation affects the quality and quantity of tear production, leading to a reduced rate of tear production.

Another factor is its effect on increasing renal blood flow, which results in the rate at which fluids are excreted from the body (diuresis).⁽⁹⁾ As observed, the effect of caffeine on tear production is short-lived, as tear production returns to near normal at the 90th minute. Nonetheless, caffeine has been observed to cause a significant reduction in tear production.

References

1. Goodman, L. and Gilman, A. (1996): The pharmacological basis of Therapeutics. 9^th The McGraw-Hill Companies, 918pp.
2. Sanford, B. and Gary Null, M. S. (1981): Caffeine: Psychological Effects, Use and Abuse. J. Orthomolecular Psychiatry, 10 (3): 202-11.
3. Bertram, K. (1995): Basic and Clinical Pharmacology. 6 Edn. Appleton and Lange, 1046pp.
4. Madder, T. H. (1991): Keratoconjunctivitis sicca caused by diphenoxylate hydrochloride with atropine sulfate. Am. J. Ophthalmol, 111:357-9.
5. Grand all, D. C. and Leopold, H. (1979): The influence of systemic Drugs on Tear constituents. J. Ophthalmol, 86:115-25.
6. Arnaud M. J. (1993). Metabolism of Caffeine and other Components of Coffee in Caffeine, Coffee and Health. New York: Raven Press.
7. Goodman L. and Gilman A. (1996).The Pharmacological Basis of Therapeutics. 9 th Edition. The Mc Graw-Hill Company.
8. Kaplan G., Greenblatt D. J., Kent M. A. and Cotreau bibbo, M. M. (1996): Caffeine Treatment and Withdrawal in Mice: Relationship between Dosage, Concentrations, Locomotor Activity and Adenosine Receptor Binding. Journal of Pharmacological and Experimental Therapeutics. 12: 1563-1573
9. Bertram G. K. (2007).Basic and Clinical Pharmacology. 10th Edition. Mc Graw Hill and Lange.