Most speech-language pathologists know enough about voice disorders to put their patients on a vocal hygiene protocol as they initiate vocal rehabilitation, but what is vocal hygiene? What does it really consist of? In addition to reducing phonotrauma, it is important to educate your patient on hydration. Hydration has been shown to improve acoustic measurements like shimmer, jitter, frequency, and maximum phonation time. This is data from a recent (2017) systematic review. We sometimes lump caffeine reduction into this "hydration" category, but what are we really telling our patients? And does the research back this up? The following is a review of studies addressing caffeine and vocal hygiene.
Back in 1999, Akhtar et al. published a study that gave us reasonable evidence to suggest that caffeine could have an effect on voice quality. The authors also stated that there was considerable intra-subject variability in the study regarding voice quality alterations. This study was relatively small at only 8 participants.
In a 2011 study by Erickson-Levendoski and Sivasankar, 16 adults were examined after consuming 480 mg of caffeine (more than double the average daily dose of 200 mg) versus 24 mg of caffeine in a beverage form. Phonation threshold pressure and perceived phonatory effort were obtained. The participants loaded themselves vocally (meaning used their voices) then were tested once more. No significant differences were found between the groups regarding voice measures. This is important because not only did caffeine not adversely affect normal voice production, it didn't make the voice any worse when the voice was taxed.
Fast forward to 2012, a pilot randomized control trial by Ahmed, Coomber, and Chetwood published in Clinical Otolaryngology posed this question about caffeine; does it result in vocal decline? Although the sample size was small, 25 people, the study looked at 2 days of 400 mg of coffee ingestion, compared with decaf, compared with water. A GRBAS (grade, roughness, breathiness, asthenia, and strain) scale was used (a purely perceptual measure), but done blindly. Alcohol, reflux, smoking and voice use were controlled for. Acoustic measures were also taken on Praat including fundamental frequency, jitter and shimmer. Though this study was limited, it did not support refraining from consuming caffeinated beverages.
In 2013, Franca, Simpson, & Schuette examined 58 females after ingesting 100 mg of caffeine. More complex software called a Computerized Speech Lab was used to gather Multidimensional Voice Program (MDVP) analysis as well as Phonatory Aerodynamic System (PAS) measures. The results? No differences after 30 minutes when tested on acoustic and aerodynamic measurements.
There is also some evidence to suggest that caffeine does not lead to fluid loss, but can irritate reflux. Regarding its specific effect on voice quality, I'd say keep your Starbucks handy if you like it!
Kristie Knickerbocker, MS, CCC-SLP, is a speech-language pathologist and singing voice specialist in Fort Worth, Texas. She rehabilitates voice and swallowing at her private practice, a tempo Voice Center, and lectures on vocal health to area choirs and students. She also owns and runs a mobile videostroboscopy and FEES company, Voice Diagnostix. She is an affiliate of ASHA Special Interest Group 3, Voice and Voice Disorders, and a member of the National Association of Teachers of Singing and the Pan-American Vocology Association. Knickerbocker blogs on her website at www.atempovoicecenter.com. She has developed a line of kid and adult-friendly therapy materials specifically for voice on TPT or her website. Follow her on Pinterest, on Twitter and Instagram or like her on Facebook.
Ahmed, S., Coomber, S., & Chetwood, T. (2012). A pilot randomised control trial: The effects of decaffeinated drinks on voice quality. Clinical Otolaryngology, 37(5), 428-431.
Akhtar, S., Wood, G., Rubin, J. S., O'Flynn, P. E., & Ratcliffe, P. (1999). Effect of caffeine on the vocal folds: a pilot study. The Journal of Laryngology & Otology, 113(4), 341-345.
Alves, M., Krüger, E., Pillay, B., van Lierde, K., & van der Linde, J. (2017). The effect of hydration on voice quality in adults: A systematic review. Journal of Voice. Advanced online publication.
Boersma, P., & Weenink, D. (2011). Praat: Doing phonetics by computer [Computer programme]. Version 5.2. 16, retrieved on 10 March 2011.
Erickson-Levendoski E. & Sivasankar M. (2011). Investigating the effects of caffeine on phonation. Journal of Voice, 25, e215–e219.
Franca, M. C., Simpson, K. O., & Schuette, A. (2013). Effects of caffeine on vocal acoustic and aerodynamic measures of adult females. In CoDAS (Vol. 25, No. 3, pp. 250-255). Sociedade Brasileira de Fonoaudiologia.
Frary, C. D., Johnson, R. K., & Wang, M. Q. (2005). Food sources and intakes of caffeine in the diets of persons in the United States. Journal of the American Dietetic Association, 105(1), 110-113.
Maughan, R. J., & Griffin, J. (2003). Caffeine ingestion and fluid balance: a review. Journal of Human Nutrition and Dietetics, 16(6), 411-420.
Verdolini, K., Min, Y., Titze, I. R., Lemke, J., Brown, K., Van Mersbergen, M., ... & Fisher, K. (2002). Biological mechanisms underlying voice changes due to dehydration. Journal of Speech, Language, and Hearing Research, 45(2), 268-281.