RESEARCH REPORT

Habitual caffeine intake in women of childbearing age E. Derbyshire & S. Abdula Faculty of Food, Clothing & Hospitality Management, Manchester Metropolitan University, Hollings Campus, Manchester, UK

Abstract Correspondence Dr Emma Derbyshire, Faculty of Food, Clothing & Hospitality Management, Manchester Metropolitan University, Hollings Campus, Old Hall Lane, Manchester M14 6HR, UK. Tel.: 0161 247 2483 E-mail: [email protected] or [email protected] Keywords caffeine, childbearing age, health implications.

Background For women, delayed conception and recurrent pregnant loss are just a few of the health implications associated with a caffeine-rich diet (Mol. Hum. Reprod., 11, 357). At present there is a deficit of prospective research measuring current habitual intakes of caffeine in UK women. The purpose of the current study was to collect up-to-date baseline data to assess caffeine intake and knowledge in a group of women (aged 16–45 years). Methods Seventy Caucasian subjects (mean age 30.4 ± 8.7 years) were recruited from business offices within the Manchester area. Each participant completed a 3-day food diary and lifestyle questionnaire. Results The mean intake of caffeine was 173.95 mg day)1 (±128.39 mg day)1). Eighteen per cent of subjects exceeded caffeine guidelines and consumed 300 mg caffeine or more each day. Subjects consuming over 300 mg day)1 were more likely to be older (P = 0.016) and smokers (P = 0.000). Individuals given previous advice about caffeine and health, had lower intakes (P = 0.002). Conclusions Many women are unaware of health perturbations associated with caffeine consumption. A diet abundant in caffeine may result in delayed conception, infertility and increased risk of osteoporosis, cardiovascular disease and cancer later in life. Such information needs to be conveyed to the public sector. Future research is also required to devise specific caffeine guidelines, particularly safe upper limits.

Ó 2008 The Authors. Journal compilation. Ó 2008 The British Dietetic Association Ltd 2008 J Hum Nutr Diet, 21, pp. 159–164

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Conflict of interests, source of funding and authorship None declared. None received. Dr Emma Derbyshire is a Senior Lecturer in Human Nutrition at Manchester Metropolitan University, specializing in Maternal Nutrition and Women’s Health Issues. Dr ED supervised this undergraduate dissertation project and facilitated with the writing of the article. SA collected and analysed the data for this article.

Introduction Caffeine is the most widely consumed stimulant in the world, 75% of which is derived from coffee (Chou, 1992). At present, consumption of coffee is often regarded as a form of socialization; a trend supporting the growth of many retailing outlets (Knight et al., 2004). One of the few studies to be undertaken (Barone & Roberts, 1996) reported that 95% of people consume a caffeine-containing beverage at least once per week. In this survey of 644 American participants, mean caffeine intake was estimated to be 4 mg kg)1 of body weight and 7.5 mg kg)1 in those consuming a high intake of tea and coffee. Research indicates that high levels of caffeine consumption may impede health status, particularly in women. Such health implications may include: infertility (Wilcox et al., 1988; Pollard et al., 1999), increased risk of miscarriage (McGill et al., 1999; Cnattingius et al., 2000; Signorello et al., 2001), cardiovascular disease (Hartley et al., 2004), high blood pressure (Lindquist et al., 1997), osteoporosis (Harris & Dawson-Hughes, 1994) and cancer (Lubin & Ron, 1990). After conception, high intakes of caffeine have also been associated with reduced foetal growth (Mau & Netter, 1974) and cot death (Ford et al., 1998). The Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment last reviewed the safety of caffeine over two decades ago (Department of Health, 1984). In this report, caffeine was categorized as safe but specific

guideline intakes were not reported (Department of Health, 1984). Furthermore, Food Standards Agency (2001) guidelines advise that only caffeine intakes exceeding 300 mg day)1 are associated with health implications. In the US the recommended upper limit for caffeine is 450 mg day)1 (Knight et al., 2004), 150 mg day)1 higher than UK guidelines. At present, such guidelines do appear to be based on a scarcity of research, and may need to be updated as our ‘coffee culture’ continues to grow and our intakes increase. In the UK, there are currently around 12 million women that are of reproductive age (between 16 and 45 years; National Statistics Office, 2006). Previous research measuring patterns and intake of caffeine have mainly used retrospective methodologies and food frequency questionnaires (Caan et al., 1998; Frary et al., 2005). Unfortunately, the accuracy of such retrospective methodologies are somewhat questionable (Biro et al., 2002). The purpose of the present study was to: (i) provide up-to-date, prospective data measuring habitual caffeine intakes in UK women of childbearing age and (ii) assess consumer knowledge about caffeine.

Materials and methods Once ethical approval was granted from a member of the University Ethics Panel (November 2006), 70 female subjects of childbearing age (16–45 years) were recruited from business offices in Manchester. After an initial meeting explaining study requirements, each participant signed a consent form, and completed a 3-day food diary (one weekend day was included) and a lifestyle questionnaire. Data from eight subjects was excluded from the main analysis. Three subjects exceeded the 45-year age limit and five subjects had not completed the food diary satisfactorily. Specific study objectives were not mentioned to the study population, to prevent reporting bias. A 3-day food diary was applied to account for day-to-day variation (Schaefer et al., 2000). Unlike food frequency questionnaires, the diet-record was open-ended, so caffeinated foods and beverages

Ó 2008 The Authors. Journal compilation. Ó 2008 The British Dietetic Association Ltd 2008 J Hum Nutr Diet, 21, pp. 159–164

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Table 1 Caffeine content of food and beverage sources

Source

Caffeine content (mg)

Median value*

Chocolate (50 g bar) Cola (330 mL can) Decaffeinated coffee (190 mL) Decaffeinated tea (190 mL) Energy drink (250 mL) Filtered coffee (190 mL) Frappuccino (270 mL) Grande Cafe´ Americano (454 mL) Grande Cafe´ Latte (454 mL) Grande Cafe´ Mocha (454 mL) Grande Cappuccino (454 mL) Grande coffee (454 mL) Grande Decaf coffee (454 mL) Herbal tea (190 mL) Hot chocolate (200 mL) Iced tea (340 mL) Instant coffee (190 mL) Short coffee (227 mL) Tall cafe´ Americano (340 mL) Tall cafe´ Latte (340 mL) Tall cafe´ mocha (340 mL) Tall cappuccino (340 mL) Tall decaf coffee (340 mL) Tea (190 mL cup)

8–25 10–50 1–5 1–5 70–90 100–150 90 174 116 166 116 372 13 40–50 10–15 26 60–75 186 116 58 58 279 10 30–60

17 30 3 3 80 125 90 174 116 166 116 372 13 45 13 26 68 186 116 58 58 279 10 45

*The median value was used in the data analysis.

could be noted without influencing reporting patterns (Biro et al., 2002). When food and beverage weights were not recorded by participants, portions sizes were administered from the Food Portion Sizes manual (Ministry of Agriculture Fisheries and Food, 1994). The caffeine content of foods and beverages was then calculated using company data (e.g. Nescafe, Starbucks and Typhoo; Table 1). Study data were analysed using the Statistical Package for the Social Sciences for analysis (SPSS, version 12.0, Chicago, IL). Descriptive statistics were calculated including the mean, standard deviation (SD) and range. The one-sample t-test was applied to compare daily caffeine intake with present caffeine guidelines (300 mg day)1). An independent-sample t-test was used to compare caffeine intake amongst women categorized into two levels of education (school education and higher education). Pearson’s correlations were undertaken to identify associations between lifestyle factors and caffeine consumption and partial

Table 2 Caffeine intakes and sources

Source of caffeine

Average intake (mg day)1)

SD

Tea (mg) Coffee (mg) Hot chocolate (mg) Carbonated drinks (mg) Confectionary (mg) Total caffeine intake (mg)

92.9 53.9 0.24 24.0 2.88 174

24.1 10.7 0.21 5.10 0.60 33.7

correlations were applied when factors needed to be controlled for (e.g. age).

Results Sixty-two subjects completed all sections of the study (a 41% response rate; 150 diaries and questionnaires were distributed at the start of the study). The mean age of study participants was 30.4 years (±8.7 years) and the range 16–45 years. Daily caffeine intake was estimated to be 173.9 mg day)1 (±33.7 mg day)1) (Table 2). The range varied from subjects that did not consume any caffeinated products to intakes as high as 535.0 mg day)1. Study findings indicated that older participants had significantly higher caffeine intakes than younger subjects (P = 0.016). Eighteen per cent of participants aged 16–25 years exceeded Food Standards Agency (2001) guidelines, 27% of females aged 26–35 years and 55% of 36–45 years exceeded this maximum threshold. Black tea was the predominant source of caffeine (43% of the daily intake), followed by caffeinated coffee and chocolate. Stimulant drinks and drinking chocolate only contributed to total caffeine intake to a small extent (Fig. 1). Mean caffeine intake was higher in smokers. Smokers consumed a mean caffeine intake of 378 mg day)1 (±78.4 mg day)1) compared to 125 mg day)1 (±80.5 mg day)1) in nonsmokers (P = 0.000). No associations, however, were identified between education level and caffeine intake (P = 0.698). Only nine (15%) of study participants had received previous information about caffeine (advice about consumption and sources). Results indicated that daily caffeine intake was lower (mean

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intake: 61 mg day)1) in participants that had received previous advice about caffeine, compared to those that had not received advice (193 mg day)1; P = 0.002). Furthermore, only 18% of participants were aware that no more than 300 mg day)1 of caffeine should be consumed during pregnancy. Subjects that identified the correct answer had lower caffeine (61 mg day)1 caffeine) intakes compared to those who answered incorrectly (198 mg day)1 caffeine) (P = 0.000).

Discussion Study findings indicate that the mean caffeine intake in women of childbearing age was 174 mg day)1 (Table 1). This was somewhat lower than figures reported previously; a factor that may be attributed to the slightly younger study population recruited in the present study. Griffiths & Woodson (1988) reported a mean daily caffeine intake of 444 mg, whilst Scott et al. (1989) calculated the mean daily caffeine intake to be 359 mg. Such disparities may also be attributed to methodological differences. Food frequency questionnaires prompt the memory and may be associated with over-reporting whilst food diaries may result in under-reporting (Biro et al., 2002). Tea was the highest contributor within the study group at 43%, followed by coffee and chocolate which contributed 17% each. A survey sponsored by the International Sweeteners Association in

1988 also found the primary contributor of caffeine intake in the UK to be tea, followed by coffee, although this study did not consider chocolate (Barone & Roberts, 1996). Similar findings were reported by Scott et al. (1989), who reported coffee and tea together account for most of the caffeine consumed in the UK. In this study, it was identified that older subjects consumed higher intakes of caffeine (P = 0.016) when compared to younger participants. Similarly, Jacobson & Bouher (1991) examined an American population sample and found a significant difference between caffeine intake and age. JohnsonGreene et al. (1988) found that older students consumed more caffeinated beverages than younger students. Conversely, Scott et al. (1989) observed that there was no association between age and caffeine intake. One plausible explanation for the higher intake of caffeine in older subjects may be to overcome symptoms of fatigue (Molarius & Janson, 2002). Smoking was also strongly associated with caffeine intake. The mean consumption of caffeine amongst smokers was more than three times higher than the nonsmokers intake. Several studies have reported similar findings (Parsons & Neims, 1978; Arnaud, 1984; Scott et al., 1989). Scott et al. (1989) observed that the mean caffeine intake of smokers was 421 mg day)1 )1 (±248 mg day ) and the mean intake for nonsmokers was 329 mg day)1 (±152 mg day)1).

Ó 2008 The Authors. Journal compilation. Ó 2008 The British Dietetic Association Ltd 2008 J Hum Nutr Diet, 21, pp. 159–164

Habitual caffeine intake in women of childbearing age

As clearance of caffeine is faster in smokers it has been proposed that higher intakes are needed to generate the same psychoactive response (Parsons & Neims, 1978; Arnaud et al., 1982; Arnaud, 1984). Parsons & Neims (1978) examined the elimination of caffeine from saliva in a group of smokers and nonsmokers. The study found that the body clearance of caffeine in smokers was greater than nonsmokers (Parsons & Neims, 1978). It is believed that smoking may double the rate of caffeine metabolism (Committee on Toxicity of Chemicals on Food, 2001). With regard to nutritional knowledge and caffeine intake, subjects that received information previously consumed less caffeine than those that had not. There is little research to support this finding from other studies. At present, the distribution of caffeine advice is rather limited in the UK. Unfortunately, as with most dietary studies, this investigation was subject to several limitations. Subjects may have under-reported their caffeine intake when food diaries were completed (Bingham, 1987). This may explain why mean daily caffeine intakes that were lower than anticipated. Within the lifestyle questionnaire the subjects were asked to state the number of certain beverages consumed per day. Comparing this answer to their food diaries showed the majority of participants had under-reported their beverage consumption. Also some individuals did not clearly state the strength, brand or amount of caffeine product they had consumed, which may greatly affect the caffeine value (Barone & Roberts, 1996). Caffeine intake would have been higher if caffeine from medications had been added to dietary intakes (painkillers can contain a much as 200 mg caffeine per tablet). It was also a limitation that the dietary analysis software could only be used to calculate macro and micronutrient intakes, but not caffeine. Although data was obtained from brand companies, different analytical methods and varying strengths of caffeinated beverages may have affected the overall results. In conclusion, this study has identified that average daily caffeine intake in UK women is only 173.9 mg day)1. However, 18% of the study population consumed in excess of 300 mg day)1.

From the study findings it appears that women know very little about caffeine guidelines and how exceeding these may impact upon female health status. Older women and smokers appear to have some of the highest intakes of caffeine. Both factors are associated with reduced fertility (older age and smoking) without accounting for caffeine consumption. Information now needs to be distributed to women of childbearing age, so the health implications of high caffeine intakes are made known into the public. Future research is required to investigate the intake of caffeine from separate sources and the health implications that these may have.

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