Coffee and health in the media

Coffee is one of the most widely consumed drinks in the world. In the UK we consume approximately 70 million cups a day¹ and spend roughly £738 million a year on our morning cappuccinos, lattes and espressos².

Despite its popularity ? and emerging research on its potential health benefits ? coffee seems to have a hard time shaking off its “bad for you” image. Just about every popular diet and detoxification regime starts with a prohibition on coffee (along with alcohol) but an explanation for this never seems to be offered. The negative image perpetuated by the media has a large impact, and healthcare professionals say they are often asked about coffee intake by patients who have read about ill-effects.

Health benefits of coffee

The British Coffee Association recommends that moderate consumption (4-5 cups per day) of coffee is perfectly safe for the general population and may confer health benefits, possibly through coffee?s antioxidant content. Coffee contains a large amount and variety of polyphenols, typically chlorogenic caffeic, ferulic and 4-coumaric acids. Roasting markedly affects the composition of the coffee polyphenols and this, and the caramelisation of carbohydrates gives coffee its taste and aroma.

A study by Richelle et al compared the antioxidant activity of coffee, cocoa and tea (including green, black and herbal) ³. The beverages were prepared in strengths that would be representative of those commonly consumed in different countries (e.g. 0.7 per cent in the USA compared to 2.0 per cent in France). The relative total antioxidant activity of the polyphenolic compounds present in each was assessed per standard cup serving, using an in vitro low-density lipoprotein oxidation model. The highest antioxidant activity was found in the coffee (and it was noted that the addition of milk did not alter antioxidant activity). The influence of the coffee bean source and the degree of roasting was also investigated, and it emerged that the green coffee beans of the Robusta plant exhibit twice as much antioxidant activity as those from the Arabica plant. After roasting, however, this difference is no longer significant.

There is limited information on the absorption and metabolism of polyphenols but a study with ileostomy volunteers shows that 30 per cent of ingested chlorogenic acid and almost all caffeic acid are absorbed in the small intestine⁴.

Diuretic properties of caffeine

Caffeine is a powerful stimulant which can counteract fatigue and improve alertness and concentration through its effect on the central nervous system⁵. However, caffeine is often unfairly criticised for its diuretic properties, and during last year?s heatwave a story in the Times on how to stay cool in the hot weather included the advice to avoid alcohol and coffee because they lead to dehydration (Times 11 August 2003). In fact, according to a study by Grandjean et al it makes no difference to the hydration status of healthy adult males whether they drink caffeinated or non-caffeinated beverages⁶.

Martof and Knox also observed no difference on hydration status measured in two groups of volunteers, the first group of whom drank caffeinated beverages on a regular basis and had developed tolerance, and the second group who habitually omitted drinks containing caffeine⁷. A study by Neuhauser-Berthold et al shows that consuming a dose of caffeine equivalent to 6 cups of coffee in a short period in volunteers with less developed tolerance does lead to negative fluid balance⁸.

The media often compare coffee unfavourably to tea, despite the fact that tea contains caffeine too. Kiyohara et al found an inverse association between coffee drinking and serum uric acid concentrations in middle-aged Japanese males⁹. The observation was attributed to the diuretic effect of caffeine in the coffee, although the relationship was not observed for green tea, another major dietary source of caffeine, which was also tested. It is generally accepted that single large doses of caffeine (250-300 mg) can have a diuretic effect, but doses at the levels commonly consumed in a serving of coffee have little or no effect, and so coffee counts towards daily fluid intake.

Coffee and heart health

Various early epidemiological studies in the 1970s linked coffee consumption to increased risk of heart disease. Today, these links remain controversial and have not been confirmed. Despite this most media stories link coffee consumption to poor health and a many column inches were devoted to Cherie Blair?s remark that the Prime Minister?s love of coffee had lead to his health scare last year. The Daily Mail (21 October 2003) reported that doctors agreed that caffeine could act as a stimulant and be a possible cause of irregular heartbeat, but failed to mention just how much caffeine would be needed cause this effect. A recent large epidemiological study failed to find an association between coffee consumption and elevated plasma homocysteine levels, known to be an independent risk factor in heart disease¹⁰.

The relationship between coffee and blood pressure has hit the headlines a number of times particularly following the results of a Greek study¹¹ investigating the effect of caffeine from coffee on wave reflection (a measure of the surge of blood as it is pumped around the body) along the arteries in the forearm. Wave reflection here is an important index of arterial stiffening and is involved in the pathogenesis of hypertension.

The researchers found that the ingestion of a single cup of coffee, containing 100 mg of caffeine, led to a substantial increase in wave reflection, stiffening the arteries for up to 3 hours, and so putting the heart under extra pressure for this period. They also observed that systolic aortic pressure increased by 3 mmHg and diastolic pressure by 6.5 mmHg. No change was observed following ingestion of a placebo. In addition, the researchers found that the first cup of coffee of the day has the most significant effect on the arteries because the residual caffeine content in the body settles to a very low level overnight. The second and third cups cause only marginal stiffening, they say.

A critical review¹² by Nurminen et al concluded that acute intake of coffee increases blood pressure, with the pressor response being strongest in hypertensive subjects. The authors reported that some studies showed a persistent pressor effect with repeated administration of caffeine, whereas in others chronic caffeine ingestion did not increase blood pressure.

Epidemiological studies have produced contradictory findings on the association between blood pressure and coffee consumption. During regular use some people develop tolerance to the cardiovascular responses, and therefore no systematic elevation of blood pressure in long-term and population studies can be shown.

Attention has not only been focused on the caffeine content of coffee. Unfiltered coffee contains the diterpenes (coffee lipids) cafestol and kahweol, which have been shown to increase LDL-cholesterol levels in human subjects¹³. When the results of this research reached the media, however, a number of the stories failed to mention that unfiltered coffee is rarely drunk in the UK.

Woodward and Tunstall-Pedoe, who looked at the tea and coffee consumption data collected from the Scottish Heart Health Study, reported a strong inverse relationship between coffee consumption and all-cause mortality, coronary death and any major coronary event¹⁴. For many conventional risk factors, coffee showed a weak, but beneficial, gradient with increasing consumption, whereas tea consumption showed the reverse. Adjustment for age and class had some effect in reducing the associations. Multiple adjustment for other risk factors removed the association for tea and most of those for coffee, although there was a residual benefit to coffee consumption in the avoidance of heart disease in men. The authors concluded that despite the pharmacological similarities between tea and coffee, epidemiological differences occurred, leading them to suggest that their multiple adjustment had been inadequate.

Coffee and pregnancy

Until recently investigations into caffeine intake and miscarriage had produced conflicting results. Headlines like “A daily coffee can increase the chances of miscarriage” (Evening Standard 17 December 2003) and “The risk to pregnant women in a cup of coffee” (Daily Mail 15 October 2003) are misleading as they suggest just one cup of coffee can increase risk, when in fact it requires a caffeine intake of over 300 mg per day (equivalent to between 2 and 4 cups).

Researchers from the University of Utah who conducted a large retrospective study reported that drinking 5 or more cups of coffee per day during pregnancy is associated with an increased risk of spontaneous abortion¹⁵. They measured serum levels of paraxanthine, a metabolite of caffeine, in 591 women who had had spontaneous abortions early in pregnancy, comparing these with 2558 matched controls who gave birth to live infants. The mean serum paraxanthine concentration was higher in the women who had a miscarriage than in controls. Women whose paraxanthine levels were equivalent to 5 or more cups of coffee were more than twice as likely to miscarry as those with lower paraxanthine levels. This effect has been supported by the results of two later studies both showing a caffeine intake of over 300 mg per day increases risk of miscarriage^{16, 17}.

The Food Standards Agency issued guidelines for caffeine consumption for pregnant women in 2001, and its current advice on caffeine intake for them, and for women wishing to conceive, is to limit their intake to 300 mg/day.

Coffee and diabetes

A study of more that 17,000 people in the Netherlands shows that those who drink at least 7 cups of coffee a day are half as likely to develop type 2 diabetes as those who drink two cups a day or fewer¹⁸. This observation was supported by The Nurses? Health Study and Health Professionals? Follow-up Study, in which researchers found that men who drink more than six cups of caffeinated coffee per day are at 50 per cent less risk of type 2 diabetes than those who do not drink coffee¹⁹. Among women, those who drink six or more cups per day reduce their risk of type 2 diabetes by nearly 30 per cent, according to the study. These effects are not accounted for by lifestyle factors such as smoking, exercise, or obesity. The study found that decaffeinated coffee is also beneficial, but its effects are weaker than those of regular coffee, an observation which is consistent with the results of two large studies in Sweden and Finland^{20, 21}.

There has been speculation that the beneficial effects may involve both improved insulin sensitivity and enhanced insulin response. A new study of coffee and diabetes²² shows that men who drink 6 cups of coffee a day reduce their chances of developing type-2 diabetes by half, while women who drink the same amount cut theirs by 30 per cent.

No doubt research into caffeine and coffee consumption and its effects on health will continue, in an attempt to establish information on the most appropriate level of consumption, and the pros and cons of drinking coffee will continue to be debated in the media, where conflicting study results are always welcome as a source of controversy. Unfortunately, the effect of this is often to cause confusion and lead to mistrust, and so it is important that those offering advice feel confident that moderate coffee intake can be part of a healthy balanced diet.

References

1 International Coffee Organization. www.ico.org

2 Coffee, Market Intelligence. Mintel International Group Ltd. January 2004.

3 Richelle M, Tavazzi I & Offord E (2001) Comparison of the antioxidant activity of commonly consumed polyphenolic beverages (coffee, cocoa, and tea) prepared per cup serving. Journal of Agricultural and Food Chemistry 49, 3438-42.

4 Olthof MR, Hollman PC, Katan MB. Chlorogenic acid and caffeic acid are absorbed in humans. J Nutr. 2001 Jan;131(1):66-71.

5 Goldberg G (2003) Plants: Diet and Health. Task Force of the British Nutrition Foundation, Blackwell Science, Oxford.

6 Grandjean AC, Reimers KJ, Bannick KE, Haven MC. The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. J Am Coll Nutr. 2000 Oct;19(5):591-600

7 Martof MT, Knox DK. The effect of xanthines on fluid balance. Clin Nurs Res. 1997 May;6(2):186-96.

8 Neuhauser-Berthold, Beine S, Verwied SC, Luhrmann PM. Coffee consumption and total body water homeostasis as measured by fluid balance and bioelectrical impedance analysis. Ann Nutr Metab. 1997;41(1):29-36.

9 Kiyohara C, Kono S, Honjo S, Todoroki I, Sakurai Y, Nishiwaki M, Hamada H, Nishiwaki H, Koga H, Ogawa S and Nakagawa K (1999) Inverse association between coffee drinking and serum uric acid concentrations in middle-aged Japanese males. Br J Nutr 82, 125-130

10 Nygard O, Refsum H, Ueland PM, Stensvold I, Nordrehaug JE and Kvale Vollset SE (1997) Coffee consumption and plasma total homocysteine: The Hordaland Homocysteine Study. Am J Clin Nutr 65, 136-143

11 Vlachopoulos C, Stefanadis C, Sofianidou A, et al. (2001) Does a cup of coffee increase wave reflection? European Heart Journal 22, 130.

12 Nurminen ML, Niittynen L, Korpela R and Vapaatalo H (1999) Coffee, caffeine and blood pressure: a critical review. Eur J Clin Nutr 53, 831-839

13 Heckers H, Gobel U and Kleppel U (1994) End of the coffee mystery: diterpene alcohols raise serum low-density lipoprotein cholesterol and triglyceride levels. J Intern Med 235, 192-193

14 Woodward M and Tunstall-Pedoe H (1999) Coffee and tea consumption in the Scottish Heart Health Study follow up: conflicting relations with coronary risk factors, coronary disease, and all cause mortality. J Epidemiol Community Health 53, 481-487

15 Klebanoff MA, Levine RJ, DerSimonian R, Clemens JD and Wilkins DG (1999) Maternal serum paraxanthine, a caffeine metabolite, and the risk of spontaneous abortion. N Engl J Med 341, 1639-1644

16 Rasch V. Cigarette, alcohol, and caffeine consumption: risk factors for spontaneous abortion. Acta Obstet Gynecol Scand. 2003 Feb;82(2):182-8.

17 Giannelli M, Doyle P, Roman E, Pelerin M, Hermon C. The effect of caffeine consumption and nausea on the risk of miscarriage. Paediatr Perinat Epidemiol. 2003 Oct;17(4):316-23.

18 van Dam RM, Feskens EJ. Coffee consumption and risk of type 2 diabetes mellitus. Lancet. 2002 Nov 9;360(9344):1477-8.

19 Salazar-Martinez E, Willett WC, Ascherio A, Manson JE, Leitzmann MF, Stampfer MJ, Hu FB. Coffee consumption and risk for type 2 diabetes mellitus. Ann Intern Med. 2004 Jan 6;140(1):1-8.

20 Agardh EE, Carlsson S, Ahlbom A, Efendic S, Grill V, Hammar N, Hilding A, Ostenson CG. Coffee consumption, type 2 diabetes and impaired glucose tolerance in Swedish men and women. J Intern Med. 2004 Jun;255(6):645-52.

21 Tuomilehto J, Hu G, Bidel S, Lindstrom J, Jousilahti P. Coffee consumption and risk of type 2 diabetes mellitus among middle-aged Finnish men and women. JAMA. 2004 Mar 10;291(10):1213-9.

22 Summaries for patients. Coffee drinkers at lower risk for type 2 diabetes. Ann Intern Med. 2004 Jan 6;140(1):I17.

Dr Sarah Schenker is a nutrition scientist at the British Nutrition Foundation