Cocoa can bring down blood pressure (BP) by inhibiting an enzyme that pushes it upwards – hence protecting the heart.
In fact, it was as effective as BP drugs designed for the same purpose, according to a new study by scientists from Linkoping University in Sweden.
Ingrid Persson, who led the study, said: “We have previously shown that green tea inhibits the enzyme ACE, which is involved in the body’s fluid balance and BP.”
Dark chocolate
“Now we wanted to study the effect of cocoa, since the active substances catechins and procyanidines are related,” the Daily Mail quoted him as saying.
Catechins and procyanidines are antioxidants that can reduce the damage oxygen can do to cells.
The team recruited a group of healthy non-smoking volunteers for the study. Two days before the study, they were not allowed to eat chocolate or anything containing similar compounds, including many berries, nor could they drink coffee, tea, or wine.
Everyone in the group gave a blood sample both before and after eating 75 grams of unsweetened chocolate with a cocoa content of 72 percent.
Scientists found ACE enzyme activity was reduced by 18 percent, three hours after the cocoa dose. This is comparable to the effect of drugs that inhibit ACE and are used as a first-choice treatment for high BP.
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Chocolate is officially “good for you”, according to The Guardian. We can now apparently rejoice at the thought that munching our Easter eggs will make us less likely to have a stroke or heart attack. The Daily Telegraph says that eating a bar a day could cut the risks by as much as 39%.
The news is based on research that followed 19,000 people over eight years. Looking at the participants’ chocolate intake at the start of the study, researchers found that higher intake of chocolate was associated with reduced risk of heart attack or stroke. However, the strength of this association was reduced when the influence of the participants’ blood pressure was taken into account. Equally, it cannot be concluded that chocolate influenced the participants’ blood pressure as it was only measured once, at the start of the study. It is also important to note that those in the highest consumption category consumed only 7.5g a day, which is far less than a whole bar of chocolate.
Overall, the question remains as to whether chocolate has any cardiovascular health benefits. It is important to remember is that, regardless of any potential benefits, chocolate is high in fat and calories and should be enjoyed only in moderation. A diet high in fat and calories is known to increase the risk of obesity, heart disease and stroke, rather than decreasing it.
Where did the story come from?
This research was conducted by Dr Brian Buijsse and colleagues of the German Institute of Human Nutrition. The study was given financial support by the German Federal Ministry of Science, the European Union and the German Cancer Aid. The study was published in the peer-reviewed European Heart Journal.
The newspapers generally did not give a balanced summary of the findings and limitations of this research, which can give no firm conclusions on the health benefits of eating chocolate.
What kind of research was this?
This was a cohort study designed to investigate the link between eating chocolate and development of high blood pressure, stroke and heart disease over an eight-year follow-up period.
A cohort study is normally a good way of observing whether a risk factor is linked to an outcome across an extended period of follow-up. However, the researchers must ensure that their cohort of participants is sufficiently large (as it was in this study) and that they account for other factors that could possibly influence their outcomes (confounders) when analysing their results. There can be particular problems with assessing dietary factors through a cohort study, namely that it is often difficult to get an accurate quantification of a person’s consumption of a particular food, and dietary habits are liable to change over time.
The preferred method for studying the effects of a substance like chocolate would be a randomised controlled trial, in which people were assigned to consume chocolate or no chocolate. However, this is likely to be unfeasible due to the large number of people and long duration of follow-up that would be needed to study cardiovascular outcomes like stroke risk. Ideally, the participants would also restrict their chocolate intake to only that which was assigned by the researchers. This seems unlikely to happen over a long study period.
If chocolate contains compounds that reduce the risk of cardiovascular disease, these substances could be extracted and tested against a placebo in randomised controlled trials.
What did the research involve?
This study used participants drawn from another study called the European Prospective Investigation into Cancer (EPIC). This research gathered data on 19,357 members of the general population, aged between 35 and 65, who took part in enrolment examinations between 1994 and 1998. All were free of cardiovascular disease and were not taking blood pressure medications. The examinations included completing a food frequency questionnaire, an interview about their medical history, lifestyle and socio-demographic details, and measurement of blood pressure and body mass index (BMI).
Chocolate consumption was assessed by how frequently a 50g bar of chocolate was consumed and how many bars of chocolate participants ate each day. In addition, 8% of the sample (1,568 people) participated in a 24-hour dietary recall assessment.
Follow-up assessments were carried out by postal questionnaire sent every two to three years. By 2004-6 (average 8.1 years), the researchers had four complete rounds of follow-up, with an average 90% response rate across all questionnaires. Self-reports of heart attack, stroke or associated symptoms were confirmed by reviewing medical records and death certificates and contacting treating physicians.
In this subsequent study, the researchers analysed the relationship between chocolate intake and cardiovascular outcomes in models adjusted for different groups of possible confounding factors. These factors included total energy intake, age, gender, alcohol intake, employment status, BMI, waist circumference, smoking, physical activity, education, diabetes, and intake of fruit, vegetables, red meat, processed meat, dairy, coffee, tea and cereal fibre.
What were the basic results?
In total, 92.3% of the sample reported chocolate consumption at the start of the study. Various factors were associated with increased chocolate intake, such as being female and having a lower intake of fruit, vegetables, dairy and alcohol. At the start of the study, reporting higher chocolate consumption was also associated with lower blood pressure (1.0mmHg average difference between the highest and lowest consumption categories). Of those who took part in the 24-hour food recall, 57% ate milk chocolate, 24% dark, 2% white and 17% did not specify chocolate type consumed.
There were 166 cases of heart attack and 136 cases of stroke during the eight-year follow-up. After adjusting for age, sex, lifestyle, BMI, diabetes and other dietary factors, those in the highest category of chocolate consumption (7.5g a day) had a 39% decreased risk of the combined outcome of heart attack or stroke compared to the lowest consumers (1.7g a day) (relative risk 0.61, 95% confidence interval 0.44 to 0.87).
Separate analysis for stroke and heart attack risk revealed significant risk reduction for stroke but not heart attack. However, adjusting for the influence of blood pressure at the start of the study reduced the strength of both associations.
How did the researchers interpret the results?
The researchers concluded that “chocolate consumption appears to lower cardiovascular risk, in part through reducing blood pressure”. They say the association appears stronger for stroke than for heart attack.
Conclusion
There are a number of important limitations that must be considered when interpreting these results:
* In this type of study, confounding factors, other than the one being assessed (chocolate consumption in this case), may contribute to the differences between the groups. Although this study took into account a number of potential confounders, it is possible that additional confounders were not measured or were inaccurately quantified. For example, lifestyle and other dietary measures were only assessed in a single measurement at the start of the study and may not reflect the participants’ histories or behaviour during follow-up.
* Although the researchers used a standard food frequency questionnaire and a 24-hour food recall questionnaire in a small sample of participants, there may still be inaccuracies in people’s recollection of their diets. Diet, including chocolate consumption, is likely to vary over a lifetime and a single assessment is unlikely to capture a person’s lifelong habits. It is also difficult to take into account the chocolate that may be included in the diet in the form of biscuits, baked goods and other sources.
* The level of chocolate consumption (estimated based on the 8% of the sample who carried out the 24-hour dietary recall) was low. For instance, those in the highest category reportedly consumed only 7.5g of chocolate a day and those in the lowest category only 1.7g. This is considerably less than the mass of the average chocolate bar, and the difference between the two groups is reported to be the equivalent of less than one small square of a 100g bar. It is unclear where the idea of a “healthy bar a day” in newspapers came from.
* Associations between chocolate and stroke or heart attack were reduced in strength when the researchers adjusted for the influence of blood pressure at the start of the study. Although the research reports that the reduced risk of heart attack and stroke may be due to the effect that chocolate has on reducing blood pressure, chocolate consumption and blood pressure were both measured at the same time in this study. This means that it cannot tell whether chocolate could have contributed to the slightly lower blood pressure at the start of the study, or whether the higher consumption group maintained lower blood pressure during follow-up.
* The researchers note that other studies on chocolate have had mixed findings, with some showing a reduction in cardiovascular disease with increasing chocolate consumption and others showing no association or only weak associations. A systematic review of all relevant studies would give a clearer picture of whether an association exists.
* As the researchers rightly say, the findings would need confirmation in randomised controlled trials. There may be some practical difficulties with this due to the long follow-up needed for measuring cardiovascular outcomes and the large participant numbers required. However, if certain compounds in chocolate (such as flavonoids) are thought to be responsible for potential cardiovascular benefits, it may be more feasible for these to be extracted and tested in randomised controlled trials.
Overall, the limitations of this study mean that it cannot conclusively prove that chocolate was directly responsible for the reduction in heart attacks and strokes. The assumption that running to the shops to eat a bar a day will stop you having a heart attack or stroke is tantalising but fanciful. However, chocolate can be enjoyed in moderation as part of a healthy, balanced diet.
High blood pressure and diabetes are both clearly associated with increased risk of cardiovascular diseases, and being overweight or obese is associated with both these risk factors. Therefore, eating a diet high in fat and calories is likely to increase, rather than decrease, your risk of these diseases.
“The blues make you crave chocolate,” according to the Daily Mail, while the BBC reports that “Chocolate lovers are more depressive”.
The news is based on research comparing symptoms of depression with chocolate consumption levels in 931 men and women. It found that participants with high depression scores ate about 12 servings of chocolate per month. Those with low scores ate an average of 8.4 servings, and non-depressed participants ate only 5.4 servings. None were taking anti-depressants.
Both news sources emphasise that the results show a potential link between chocolate and depression. But they highlight that, by design, it was unable to say whether chocolate caused depression or the other way around. Only a large study that follows the eating habits of many people over time could test which of these theories is true.This should perhaps be the next step in chocolate research.
Where did the story come from?
This research was carried out by Dr Natalie Rose and colleagues from the University of California in San Diego. The study was funded by grants from the National Heart, Lung and Blood Institute of the US National Institutes of Health. The study was published in the peer-reviewed medical journal Archives of Internal Medicine.
The Times and Metro appropriately highlighted the finding that consuming other antioxidant-rich substances, such as fish, coffee, fruits and vegetables, had no bearing on mood. This suggests that the findings are specific to chocolate.
What kind of research was this?
This was a cross-sectional study looking at the relationship between the average quantity of chocolate eaten per week (assessed by questionnaire) and depressed mood, which was assessed by using a validated pyschological scale called the Center for Epidemiologic Studies Depression Scale (CES-D).
The depression screening scale divided participants into three groups: those with probable major depression, those screening positive for depression but not major depression, and those who were unlikely to have depression. In addition to the depression screening questionnaires, participants were asked two questions about their chocolate consumption: ‘how many times a week do you consume any chocolate?’ and ‘how many servings a month do you consume?’.
A serving was considered to be one small bar or one ounce (28g) of chocolate. Smaller and larger quantities were defined in relation to this medium serving: a small serving was half the size of a medium one, while a large serving was equivalent to one and a half times the medium.
The survey was cross-sectional and used subjective measures of chocolate consumption (estimated through questionnaires). This means that it has several limitations that make it unable to prove that chocolate causes depression or that depressed people eat chocolate to make themselves feel better.
What did the research involve?
The authors of this study say that chocolate is constantly proclaimed to have benefits on mood, but they are surprised by the lack of robust studies directly examining the link between chocolate consumption and mood in humans. To research this relationship, the authors drew data from a study that examined the non-cardiac effects of reducing cholesterol levels.
They recruited a total of 1,018 participants aged 20 to 85 years (694 men and 324 women) from San Diego. They excluded people with known vascular disease, diabetes, high/low levels of cholesterol, or those taking anti-depressants (78 people).
The participants were asked to complete food questionnaires and a depression screening questionnaire. After excluding people who did not complete both questionnaires, 931 people were available for analysis.
One food questionnaire, the SSQ-C, simply asked participants how many times a week they consumed chocolate. The second was a more intensive Food Frequency Questionnaire (FFQ-C), which asked about the absolute frequency of any chocolate consumption (times per month) and the amount of chocolate consumed (servings per month). Responses on daily or monthly consumption were converted into per-month consumption estimates to provide a measure that could be compared across the questionnaires. The FFQ also asked about other foods and nutrients, including intake of carbohydrates, fat and energy.
The researchers also administered the Center for Epidemiologic Studies Depression Scale (CES-D) tests, which asks participants about 20 symptoms of depression, and scores each of their answers on a scale of four (zero to three), giving a maximum score of 60. The scale measures depressive feelings experienced during the previous week.
The researchers analysed the data appropriately, using cut-off points to indicate minor depressive symptoms (above 16 but less than 22) and more major symptoms to indicate a depressive disorder (more than 22). Anyone scoring less than 16 was considered to be free of depression. The results of this analysis were not adjusted for the influence of other food intake, although the researchers did do similar analyses for fat, energy and carbohydrate.
What were the basic results?
The average age of participants was 57.6 years, and their average BMI was 27.8.
The average CES-D score was 7.7, ranging from 0 to 45 (maximum possible score 60). Average chocolate consumption for the whole group was six servings per month, with participants eating chocolate on six occasions per month.
Participants with a CES-D score of 16 or higher reported significantly more chocolate consumption (8.4 servings per month) compared to those with lower CES-D scores of less than 16 points (5.4 servings per month). The group with the highest CES-D scores (22 or higher) had even higher chocolate consumption (11.8 servings per month). These differences between the groups were statistically significant.
In contrast to the findings on chocolate, differences in fat, energy or carbohydrates intakes in each CES-D group were not significant. This suggests that it is specifically chocolate that has a relationship with mood rather than other foodstuffs.
How did the researchers interpret the results?
The researchers say that “higher CES-D depression scores were associated with greater chocolate consumption. Whether there is a causal connection, and if so in which direction, is a matter for future prospective study”.
Conclusion
This study will be of interest to many, but unfortunately it has not resolved the debate about whether depression causes people to eat chocolate or if people take chocolate to relieve low mood. The amount of chocolate eaten (six servings a month on average) may be seen as relatively little by some regular chocolate consumers. The authors acknowledge several limitations:
* As the study was conducted for a different initial purpose, (looking at vascular disease) it is possible that some groups of participants were excluded because of vascular disease or age. This may have skewed the selection of participants, making them unrepresentative of a general population.
* The study was based on a self-report of diet and chocolate and other nutrient consumption. This could have introduced some error or bias in that many people cannot accurately recall or estimate an average consumption of these items. As a general food frequency questionnaire was used, the participants may not have been aware of the importance of the chocolate question.
* The CES-D screening scale is a tool for picking up symptoms that need further evaluation; it does not indicate a diagnosis of depression according to the accepted criteria. It does indicate an increased risk, however it is not correct to say that a link with ‘depression’ has been proven.
* Different chocolate preparations were not assessed. Neither were some of the contents of chocolate that are thought to underlie the effect. The researchers mention that certain specific substances that naturally occur in chocolate (phenylethylamine, anandamine or theobromine) could be examined in future studies.
Overall, this study shows that people who screen positive on a depression screening scale eat more chocolate than those who do not. To determine whether the link is causative, people will need to be tested in long-term studies that objectively assess chocolate consumption at the start of the study and follow people to observe how depressive symptoms develop over time.