Nutritional knowledge and intake of caffeine-containing beverages among pregnant and breastfeeding women

Introduction

Caffeine is a naturally occurring substance found in the leaves of the tea plant, mate, coffee beans, and cocoa. It is most often consumed in the form of infusions of coffee, tea, chocolate, cocoa, or beverages with its addition, including cola drinks and energy drinks [1]. Orally administered caffeine is rapidly absorbed and distributed throughout the whole body, reaching maxi­mum plasma concentration after 30-45 minutes and exhibiting a half-life of 5 to 6 hours in plasma. In pregnant women, as pregnancy progresses, there is a reduction in maternal caffeine clearance, which results in an extension of the caffeine half-life and increased foetal exposure to this substance. Increased foetal exposure to caffeine may result in uteroplacental vasoconstriction and foetal hypoxia due to the underdeveloped liver and lack of the CYP1A2 enzyme, which prevents the foetus from metabolising caffeine [2]. High caffeine intake during pregnancy has been associated with an increased risk of low birth weight [3] and even behavioural disorders in offspring [4]. Caffeine consumed by the mother is transferred to breast milk, and the half-life of caffeine is longer in infants during the neonatal period, with even more delayed elimination in breastfed infants [5, 6]. The human hepatic metabolic capacity is only achieved at approximately 5 to 6 months of age. Prior to this, the immature expression of the hepatic metabolic system will result in a longer half-life for caffeine [2]. Conversely, caffeine is not entirely contraindicated in infants. The stimulant effects of caffeine are utilised clinically for the treatment of apnoea of prematurity [7]. It is uncertain whether caffeine consumption impacts the length of lactation in nursing mothers because there is a lack of conclusive data on this matter [8].
Coffee and tea account for over 90% of caffeine consumption. In countries where these beverages are consumed, the average daily caffeine intake of adults is approximately 200 mg [6]. The value falls within the safe intake range, as established by the European Food Safety Authority (EFSA) for general populations of adults, which specifies a maximum daily intake of 400 mg (5.7 mg/kg body mass per day ) [9]. The 2020 recommendations on dietary guidelines for the general Polish population from the National Centre for Nutrition Education include no quantitative recommendations regarding coffee and tea consumption. However, the recommendations do acknowledge the hydration benefits of tea and coffee because these beverages are presented together with water [10]. The following recommendations are directed towards the general population. In the case of pregnant or breastfeeding women, a more restrictive caffeine limit is advised, with an upper limit of 200 mg per day [9]. In light of the data on caffeine content in popular beverages, as outlined by the EFSA, this equates to approximately 3 cups (150 ml) of ground coffee, 3 espressos (50 ml), or 2 glasses (250 ml) of ready-to-drink instant coffee. It is important to note that the caffeine content of coffee beverages can vary significantly even within the same country. These differences are due to the roasting me­-thod, the type of coffee beans used, and the preparation method (e.g. drip coffee, espresso) [9]. The educational materials for pregnant women developed by experts from the Institute of Mother and Child highlight the importance of limiting caffeine consumption, with an upper limit of 1-2 cups of coffee per day, as recommended by medical professionals [11]. In contrast, the Food Pyramid for breastfeeding women published in 2023 allows for the consumption of 6 cups of coffee or 10 glasses of tea per day [12].
In light of the lack of clear guidance on the consumption of food sources of caffeine in the diet and its potential adverse effects at higher doses, it is crucial to monitor caffeine intake in vulnerable groups, particularly among pregnant and breastfeeding women. Identifying factors that may increase the risk of excessive caffeine intake could enhance the efficacy of educational initiatives.
The objective of the study was to evaluate caffeine intake from typical caffeinated beverages among pregnant and lactating women. Furthermore, the relationship between the level of nutritional knowledge and selected socioeconomic and demographic indicators and the amount of caffeine was examined.

Material and methods

A descriptive cross-sectional study was carried out between September and November 2023 using the Computer-Assisted Web Interview (CAWI) method. Purposive and convenience sampling was used: pregnant and lactating women were included in the study. Participants were recruited through thematic Internet forums and snowball sampling. The study was voluntary and anonymous. No information was collected that could identify participants. Consent to participate in the study was given by agreement to complete the survey. The protocol adhered to the tenets of the Declaration of Helsinki for research involving human participants. The survey was designed to be self-administered, allowing respondents to complete the questionnaire independently. A total of 304 individuals participated in the study, of whom 63 gave responses that were deemed invalid (for example, due to the entry of a letter in a question where participants were asked to enter a number, or the number was highly incredible). Additionally, 2 women were excluded from the study due to concurrent pregnancy and breastfeeding.
To quantify caffeinated beverage consumption a food- specific frequency questionnaire with daily, weekly, and monthly frequency options based on the KomPan questionnaire [13] was used, along with questions regarding the usual portion size of beverages. For calculation, the following portion sizes were used: (a) in the case of self-prepared coffee, tea, and cocoa, the respondents entered the size of the portion used in teaspoons (1 teaspoon = 2.5 g coffee beans, ground, 2.0 g instant coffee, tea leaves, cocoa powder; 1 tea bag = 2.0 g), regardless of the amount of infusion made from it; (b) in the case of other beverages: sizes from 50 ml up to 0.5 l in increments of 50 ml. In the case of the latter, respondents were given the option of selecting from a range of coffee beverages, including Americano, cappuccino, latte, and espresso. For each participant, the daily average consumption of beverages prepared from ground roast coffee beans, instant coffee extracts, and other coffee-based beverages, tea (black, white, and green), mate, as well as the consumption of coffee-flavoured beverages (cola-based soft drinks, iced teas, or energy drinks) and cocoa drinks was calculated. The caffeine content of the beve­rages was determined to be the average caffeine concentration set forth in the Scientific Opinion published by EFSA [9] or according to the nutrients database [14-17] with the exception of those where the caffeine level was indicated on the packaging labels (Table 1). Based on the aforementioned data, the daily caffeine consumption (in milligrams) was calculated and compared with the dose considered by the EFSA [9]. Furthermore, the median caffeine intake was calculated for women who exceeded the recommended safe intake level.
The level of general nutritional knowledge was eva­luated through the administration of a validated questionnaire comprising 25 statements pertaining to food and nutrition. Participants were instructed to select one of three responses: “yes”, “no”, or “I don’t know”. The correct answer was assigned a value of 1, while incorrect or “I don’t know” responses were assigned a value of 0. A total score ranging from 17 to 25 points was indicative of a good level of knowledge, a score between 9 and 16 – sufficient, and 0 and 8 – insufficient level of general nutritional knowledge [13].
To assess knowledge of the safety of caffeine consumption during pregnancy and lactation, the questionnaire was supplemented with items relating to the respondents’ self-perceived knowledge of nutrition and correct eating habits, their understanding of safe levels of caffeine consumption during pregnancy and lactation, and their use of advice from a dietician during this period.
The sociodemographic questions characterising the study group were derived from the KomPan questionnaire and self-reported [13]. Body mass index (BMI [kg/m2]) was calculated based on self-reported data from the pe­riod before pregnancy/lactation [18].
Statistical analysis was conducted using StatSoft Statistica 13.1 software. For quantitative data with non-normal distribution, the U-Mann-Whitney or Kruskal-Wallis tests were employed, while for qualitative data, the Pearson c2 test was utilised. A significance level of p < 0.05 was assumed to indicate the presence of statistically significant differences or relationships.
The research complies with all the relevant national regulations and institutional policies, and it is in accordance the tenets of the Helsinki Declaration. The study was anonymous, participants were presented with its purpose and scope, and they were also given information on the possibility of discontinuing the survey at any stage. Returning the survey was tantamount to giving informed consent to use the data for scientific purposes.

Results

The number of individuals ultimately qualified for the study was 239 women, of whom 80 were pregnant and 159 were breastfeeding. The average age for the total group was 30.3 ± 5.04 years; the mean age of the pregnant women was found to be significantly lower than that of the breastfeeding women (28.8 ± 4.60 vs. 31.0 ± 5.10, respectively; p = 0.002). The mean BMI was similar across the groups (23.08 ± 3.36 vs. 23.18 ± 2.76 for pregnant and breastfeeding women, respectively; p = 0.406). The sociodemographic characteristics of the studied group are presented in Table 2.
The majority of women lived in large cities and had higher education. These characteristics did not diffe­rentiate pregnant and breastfeeding women. The labour market status of the 2 groups was clearly differentiated: the vast majority of pregnant women were employed, while the majority of breastfeeding women were on leave. Similarly, there were significant differences in the economic situation. Pregnant women most often rated it as above average, while breastfeeding women indicated it as average. Over half of the women were pregnant for the first time, and more than one-third of the breastfeeding women were doing so for the first time.

The general nutritional knowledge and awareness of the safe dose of caffeine

Table 3 presents the parameters that characterise the level of nutritional knowledge and awareness of safe doses of caffeine intake among the examined women.
The surveyed women, both pregnant and breastfeeding, demonstrated a high level of confidence in their nutritional knowledge (72% very good and good answers among pregnant women, and 67% among breastfeeding women) with no differences between groups. This was confirmed by the results of the objective assessment of general nutritional knowledge, which demonstrated that 86% of pregnant women and 87% of breastfeeding women exhibited a good level of knowledge in this area. There was a discrepancy between the 2 groups in their understanding of the maximum safe amount of caffeine for pregnant women. Pregnant women were 6 times more likely to overestimate the safe amount than those who were breastfeeding (24% vs. 4%). Although a similar proportion of women in both groups correctly identified the maximum safe amount of caffeine for breastfeeding women, a larger proportion of breastfeeding women reported a lack of such knowledge (23% vs. 8%, respectively). A significant proportion of pregnant women (approximately one-third) believed that coffee consumption should be avoided during this period. However, a similar percentage (30%) indicated that one cup of coffee per day was safe. In the case of breastfeeding women, two-thirds indicated that one cup of coffee per day is safe, and only 10% believed that coffee should be avoided. No differences were found in knowledge regarding maximum coffee consumption among breastfeeding women between the examined groups.

Daily caffeine intake

The median daily caffeine consumed among all the exa­mined women was 104.3 mg (mean 117.8 ± 102.98 mg/d). Figure 1 shows the share of caffeine-containing beverages in the women’s diets. The primary sources of caffeine in the diets of the surveyed women were coffee and tea, which together constituted 92% of the caffeine intake among pregnant women and 95% among breastfeeding women.
In 84% of the entire group (pregnant women 90%, breastfeeding women 81%), the intake was found to be within the safe range (< 200 mg/d). The median caffeine intake for the group mentioned above was 78.9 mg per day (range: 0.0-197.2 mg/d), while for women exceeding the recommended safe level, it was 265.5 mg per day (range: 200.7-690.9 mg/d). Detailed information on estimated daily caffeine intake in the studied group is pre­sented in Table 4.
The study revealed no significant differences in average caffeine consumption between pregnant and breastfeeding women (105.9 ± 95.3 mg/d vs. 123.8 ± 106.4 mg/d). Additionally, the analysis did not identify any notable variations when factors such as previous pregnancies/lactation, nutritional knowledge, awareness of the safe dose of caffeine, and experience with dietitian care were taken into account. Furthermore, no significant relationship was observed between the safe level of caffeine consumption and the following variables: education (p = 0.779), general nutritional knowledge (p = 0.667), the correctness of estimating the safe amount of coffee consumption for pregnant (p = 0.543) and breastfeeding women (p = 0.226), and contact with a dietician (p = 0.592).

Discussion

Caffeine is one of the most common substances consumed in pharmacologically active amounts worldwide, and as a result, it is the subject of numerous studies that assess the potential benefits [19-23] and risks associated with its consumption in different population groups [24-26]. Based on scientific data and according to the latest EFSA scientific report, caffeine consumption at a level of 400 mg per day does not pose safety concerns for healthy adults in the general population, with the exception of pregnant and breastfeeding women, for whom this threshold is reduced to half of this value [9]. However, as caffeine is a habit-forming substance, its habitual consumption leads to physical dependence, indicated by behavioural, phy­siological, and subjective withdrawal effects in response to abstinence [27-29]. This may present a challenge to the restriction of caffeine consumption during the perinatal period, despite the awareness of such recommendations. Conversely, recommendations expressed in terms of caffeine content may prove challenging for individuals with limited nutritional knowledge to comprehend.
In the present study the average daily caffeine intake among the 80 pregnant women was 105.9 mg (median 106.9), and 123.8 mg (median 104.3) among the 159 breastfeeding women. These values were comparable to those previously reported by Lisowska et al. [30] and Jarosz et al. [31] in the case of pregnant women (114.5 mg and 91.0 mg, respectively), as well as by Pituch et al. [32] in the context of breastfeeding (127.4 mg). How­ever, in the aforementioned study, this value was obtained using the 3-day food record method. When the food frequency questionnaire was used to calculate caffeine intake, the value was higher (163.4 mg). The most recent Polish survey from 2023, conducted among 711 breastfeeding women, demonstrated an even greater value – 193.7 mg/day [30]. However, it is important to note that the authors also assessed caffeine intake from chocolate and took into account the time of brewing tea, which could have affected their score. It is noteworthy that there is a dearth of data on caffeine consumption by breastfeeding women in Poland, warranting further investigation. A comparison of the obtained values with data from other countries reveals some differences, which can be attributed to variations in dietary patterns. The mean caffeine consumption among Greek women who were breastfeeding was approximately 51.1 and 53.9 mg at 3 and 6 months postpartum, respectively [33], whereas the mean consumption among postpartum women from Argentina was 350.6 mg – with the highest share of caffeine from Yerba mate [34]. A greater body of evidence from the literature concerns the consumption of caffeine by women during pregnancy [30, 35-39], but in this case also there are few surveys conducted in Poland. Regarding the results of the other Polish studies, the obtained values were similar [30, 31] or higher [35, 36]. Nevertheless, the observed average amount of caffeine consumed by pregnant and lactating Polish women is less than that consumed by the general population of women [40, 41], which clearly indicates a reduction in dietary sources of caffeine in these physiological states.
Even those who are aware of the maximum safe dose of caffeine may encounter difficulties in adhering to these recommendations, largely due to a lack of awareness about the potential dietary sources of caffeine and its content in food products.
Nutritional knowledge plays a crucial role in shaping eating habits and, subsequently, may influence caffeine consumption. Nevertheless, despite a high self-assessment of nutritional knowledge and favourable results on an objective knowledge test, a considerable proportion of the surveyed women demonstrated an inability to correctly indicate a safe dose of caffeine for pregnant and lactating women. The proportion of correct responses was less than that observed in the study by Lisowska et al. [30]. It is noteworthy that more women provided responses that were below the recommended threshold compared to the share of women choosing the higher amounts. This may indicate that women have an intui­tive understanding of the detrimental effects of excessive caffeine consumption, despite their inability to give specific quantities. It is also important to note that knowledge of the precise quantity of caffeine is a specialised area of expertise. It is more crucial for women to be aware of the amount of coffee, tea, and other caffeinated products they can consume than to be informed of the recommended milligram intake. Lisowska et al. [30], Malczyk et al. [41], and Wierzbicka and Momot [40] identified coffee as women’s main dietary source of caffeine. Assuming that the average cup of coffee contains about 66 mg of caffeine [41], its safe amount is 2-3 cups. This response was deemed correct by slightly more than a quarter of the group. It is noteworthy that a greater number of women indicated a lower quantity or even the necessity to eliminate coffee from the diet (in the case of a pregnant woman). Other studies also point to the phenomenon of reducing or even eliminating coffee (and caffeinated beverages) from the diet of pregnant and lactating women [30, 32]. The recommendations in popular media for pregnant and breastfeeding women to consume caffeine in moderation and in reasonable amounts during this period are subjective and may therefore be interpreted in different ways by different individuals.
In summary, not all pregnant and breastfeeding women in this study consumed the reported safe level of 200 mg of caffeine per day. While many consumed less or none at all (2.5% of the total group), a significant proportion regularly consumed more (10% of pregnant women and 19% of breastfeeding women). Although the vast majority of women did not consume energy drinks or caffeinated soft drinks (both of which are high in caffeine), it appears that habitual consumption of both coffee and tea may pose a risk of exceeding the safe dose.
The strength of this study is the qualitative and quantitative assessment of caffeine consumption. Individual preferences for beverage preparation were taken into account, and respondents were able to choose between many different portion sizes. Additionally, the study included an analysis of general nutrition knowledge using a validated questionnaire, as well as an assessment of knowledge of a safe dose of caffeine and a serving of coffee. Limitations of the study include unequal groups, which was a hindrance when comparing results. As the data on caffeine were self-reported and obtained via questionnaire, it is unavoidable that exposure misclassification of coffee/caffeine intake will occur. The data concerning caffeine content were derived from existing literature, and the analysis was limited to beverages. Although respondents were assured of anonymity and the option to decline participation in the study, the remote nature of the survey may have introduced the potential for inaccurate responses.

Conclusions

While the majority of the group did not exceed the safe level of caffeine estimated for caffeinated bever­age consumption, in individual cases this level was exceeded by up to 3-fold. Tea, despite its lower caffeine content, was the second largest source of caffeine due to its larger portions and frequency of consumption. Therefore, it should not be excluded from nutritional education for pregnant and breastfeeding women. A good and sufficient level of general nutritional knowledge does not necessarily imply the capacity of the surveyed women to ascertain the safe consumption of caffeine or coffee. This suggests the continued necessity to enhance women’s awareness of the potential risks associated with excessive caffeine consumption and to promote moderation of this substance during pregnancy and lactation.

Conflicts of interest

The authors declare no conflict of interest.

References