Resveratrol's health benefits 'overstated'

“Red wine health benefits 'overhyped',” BBC News reports. The headline follows a study researching the chemical resveratrol, which is found in red wine and chocolate.

Reveratrol has been reported to have long-term health benefits, such as anti-inflammatory and anti-cancer effects. There has been speculation that it may be responsible for the “French paradox”: the puzzling fact that rates of heart disease are low in France, despite citizens enjoying a rich diet.

This study involved almost 800 people from the Chianti region of Italy. The researchers wanted to see if resveratrol had any links with cancer, cardiovascular disease and death rates.

The study found that the risk of death during the nine-year follow-up period was no different for people with the highest levels of metabolites (breakdown products) of resveratrol in their urine, compared to people with the lowest levels. There was also no difference in the risk of developing cancer or cardiovascular disease.

However, red wine and chocolate contain more than just resveratrol. They may still be good for you (in moderation), but this study suggests that resveratrol may not be the reason why.

Where did the story come from?

The study was carried out by researchers from the John Hopkins University School of Medicine, the National Institute on Aging and the New England Research Institute in the US; the University of Barcelona and Catalan Institute of Oncology in Spain; and the Istituto Nazionale di Riposo e Cura per Anziani V.E.II.–Istituto di Ricovero e Cura a Carattere Scientifico and the Azienda Sanitaria in Italy. It was funded by the US National Institutes of Health and National Institute on Aging, the Italian Ministry of Health and the Spanish Government.

It is unclear why the research focused on an area that is famous for its red wine. However, it must be noted that this was part of the long-running “InCHIANTI” study, which has produced dozens of published research pieces.

The study was published in the peer-reviewed medical journal JAMA Internal Medicine.

This story was widely covered by the press, with most of the headlines focusing on chocolate and red wine. It should be noted that these contain more than just resveratrol – the chemical studied in this research. Resveratrol is also found in a wide range of foods.

Finally, it is somewhat amusing that some newspapers talk dismissively of the “resveratrol myth” – the idea that resveratrol is good for you – as these are the very same newspapers that promoted the idea in the first place.

What kind of research was this?

This was a cohort study that aimed to determine if resveratrol levels, measured from the levels of metabolites (breakdown products) in urine, were associated with cancer, cardiovascular disease and death rates.

Cohort studies can show association, but cannot show causation. It should be noted that there were significant differences between people with different resveratrol metabolite levels in their urine. For example, those with the highest metabolite levels were less likely to have cognitive impairments.

Although the researchers tried to adjust for these confounding factors, they could still affect the results of this study.

What did the research involve?

In this study, 783 people aged 65 years or older from two villages in the Chianti area in Italy were followed between 1998 and 2009, to see if they:

died
developed cancer
developed cardiovascular disease

The researchers examined whether these outcomes were associated with the level of resveratrol metabolites in urine. Resveratrol metabolites in urine samples collected over 24 hours were measured at the beginning of the study.

The researchers took the following confounders into account:

age
sex
education
body mass index (BMI)
physical activity
total energy intake
total cholesterol
high density lipoprotein (HDL) cholesterol
Mini-Mental State Examination (MMSE) score – a measurement of cognitive ability
average arterial blood pressure
chronic diseases

What were the basic results?

During the nine-year follow-up period, 268 (34.3%) of the people studied died.

The researchers compared the risk of death during follow-up for people with the lowest 25% of resveratrol metabolites in their urine to those with the highest 25%, and found no significant difference in the risk of death.

To confirm this result, the researchers looked at the relationship between the dietary intake of resveratrol (assessed from a food frequency questionnaire) and the level of resveratrol metabolites in urine.

These were correlated, meaning that people with the highest dietary intake had the highest levels of metabolites in their urine.

The researchers also found that people with the lowest 25% of dietary intake of resveratrol did not have a significantly different risk of death during follow-up, compared to people with the highest 25% of intake.

They then studied whether resveratrol metabolite levels in urine were associated with the development of cardiovascular disease and cancer in people who did not have these diseases at the beginning of the study.

Again, resveratrol metabolite levels in urine were not significantly associated with the development of cardiovascular disease or cancer during the study.

How did the researchers interpret the results?

The researchers conclude that “this prospective study of nearly 800 older community-dwelling adults shows no association between urinary resveratrol metabolites and longevity. This study suggests that dietary resveratrol from Western diets in community dwelling older adults does not have a substantial influence on inflammation, cardiovascular disease, cancer or longevity”.

Conclusion

This study of almost 800 older adults in Italy found that the risk of death during a nine-year follow-up period was no different for people with the highest levels of metabolites of resveratrol in their urine, compared to people with the lowest levels. There was also no difference in the risk of developing cancer or cardiovascular disease.

Although this was a well-designed study, it should be noted that:

cohort studies cannot show causation. There were significant differences between people in the different categories of resveratrol metabolite levels. For example, people with high resveratrol metabolite levels were more likely to be male, smoke and be physically active. They were also less likely to have cognitive impairment. This could complicate matters – while physical activity is linked with better health, smoking may have counteracted the positive effects of resveratrol.
resveratrol levels were only measured once, over 24 hours at the beginning of the study. This may not be representative of the participants’ usual pattern of consumption of red wine, berries and chocolate.
the study compared people with different resveratrol metabolite levels. It may be the case that there is a threshold level over which resveratrol has an effect, although the researchers say they don't know of one.

It should be noted that red wine and chocolate contain more than just resveratrol. They may still be good for you, but this study suggests that resveratrol may not be the reason why.