Month: December 2012

A tomato a day keeps depression at bay

The Daily Mail today reported that there is, “yet another good reason to tuck into that salad: eating tomatoes could ward off depression”.

Tomatoes are rich in lycopene, the chemical that gives them their distinctive colour. Lycopene is an antioxidant, a type of naturally occurring chemical believed to help protect against cell damage.

 

Previous research suggests foods high in antioxidants could have a preventative effect against physical diseases such as strokes. In this study, the researchers were interested in seeing if a similar preventative effect could also apply to depression.

The researchers assessed the mental health and dietary habits of 986 Japanese people aged over 70 years. They found that those who reported eating tomatoes two to six times a week were 46% less likely to report mild or severe symptoms of depression than those who said they ate tomatoes less than once a week. No such association was found for other vegetables.

This study has many limitations to consider, including a potential error in the way they measured dietary intake. Crucially, an inherent weakness of this type of research (a cross-sectional study) is that it can’t prove a direct cause and effect between reported tomato consumption and mental health.

It can also be subject to confounders. For example, it could be that in some cases, people who eat a lot of fresh fruit live a healthier lifestyle and take lots of exercise – and the exercise could be having the beneficial effects on mental health.

With those caveats in mind, this study is consistent with the advice that eating a healthy, varied and balanced diet is beneficial for both physical and mental health.

Where did the story come from?

The study was carried out by researchers from Japanese and Chinese universities and was funded by grants from the Japanese Ministry of Education and Ministry of Health and the Japan Arteriosclerosis Prevention Fund. No conflicts of interest were declared.

The study was published in the peer-reviewed Journal of Affective Disorders.

The media coverage of the study was balanced and included a useful testimony from the researchers indicating that they could not be sure if lycopene in tomatoes directly affects the mind.

What kind of research was this?

This was a cross-sectional survey looking at the potential link between intake of vegetables and tomato products and depression.

The researchers state that defective antioxidant defences are related to symptoms of depression. That is, people who are more vulnerable to cell damage caused by ‘rogue’ molecules called free radicals, may also be more prone to experiencing depressive symptoms.

They were interested to investigate whether vegetables, which are known to be good sources of antioxidant chemicals, may have a protective effect. They were particularly interested in lycopene, a powerful antioxidant present in high levels in tomatoes.

Cross-sectional studies can only highlight associations – they cannot prove cause and effect (in this case, they can’t prove that eating tomatoes causes less depression or protects against it).

Depression and its causes are complex. The causes may include genetics, environment, and personal circumstances. Additional factors, outside of antioxidant intake, influence this relationship and this type of study is unable to account for them all.

What did the research involve?

Information on 986 ‘community dwelling’ (not in hospital or residential care) elderly Japanese individuals aged 70 years and older was analysed in this study. Participants were living in one of the major cities in the Tohoku area of Japan.

The participants’ dietary intake was assessed using a validated self-administered diet history questionnaire. This required participants to indicate the average frequency they ate each of a list of 75 food items over the past year, ranging from “almost never” to “two or more times per day”.

The questions on tomatoes included fresh tomatoes as well as tomato products such as tomato ketchup and “tomato stew” – a Japanese dish consisting of beef stewed in tomato juice.

Other vegetables were categorised into:

  • green-leaf vegetables
  • cabbage and Chinese cabbage
  • carrot, onion, burdock, lotus root and pumpkin
  • Japanese white radish (daikon) and turnips

Tomato and tomato product consumption was then categorised into three separate consumption groups:

  • one or fewer servings per week
  • two to six servings per week
  • one or more servings per day

Depressive symptoms were evaluated using a Japanese version of a 30-question Geriatric Depression Scale (GDS). The scale used two cut-offs: 11 (mild and severe depressive symptoms) and 14 (severe depressive symptoms). Participants were also categorised as having mild or severe depression if they used anti-depressive drugs.

Numerous other measures were taken, including:

  • height
  • body weight
  • blood pressure
  • indicators of past health
  • current medication intake
  • sociodemographic variables such as age, gender, and educational level
  • perceived social support – for example, was there a friend or relative readily available if a participant fell ill

Participants with no information on diet, or who had a history of cancer or impaired mental ability, were excluded from the study.

The analysis compared differences in tomato and vegetable intake to see if they were significantly related to reports of depressive symptoms. Depressive symptoms were defined as mild or severe depressive symptoms (GDS of 11 or more) or use of antidepressants.

What were the basic results?

The prevalence of mild and severe depressive symptoms in the group was 34.9% when combined and 20.2% for only those categorised as severe.

There were significant differences in the baseline characteristics of those reporting different tomato consumption levels for a range of variables, including gender, smoking status, education level and marital status, and others.

Tomato consumption seemed high in this population as there were:

  • 139 (14%) people in the one or fewer servings per week group
  • 325 (33%) in the two to six servings per week group
  • 522 (56%) in the one or more serving per day group

After adjustment for potentially confounding factors, the relative risk of having mild and severe depressive symptoms (combined) was 52% less in those eating tomatoes or tomato products once or more each day, compared with those reporting consumption of once a week or less (odds ratio (OR) 0.48 95% confidence interval (CI) 0.31 to 0.75).

The risk reduction was slightly less (46%) for those eating two to six servings of tomatoes or tomato products compared to those reporting consumption of once a week or less (OR 0.54, 95%CI 0.35 to 0.85).

The analysis showed a statistically significant trend (p<0.01) linking higher tomato consumption to lower levels of depressive symptoms.

Similar results were obtained when they considered only severe depressive symptoms (GDS of 14 or more) which showed a 40% reduction in those eating tomatoes or tomato products once or more each day compared with those reporting consumption of once a week or less (OR 0.60, 95% CI 0.37 to 0.99).

The analysis reported here was adjusted for the confounders discussed above, as well as:

  • smoking and drinking habits
  • physical activity
  • cognitive status
  • self-reported body pain
  • total energy intake
  • reported intake of all kinds of fruits, green tea, and vegetables

No significant relationships were observed between intake of other kinds of vegetables and depressive symptoms.

How did the researchers interpret the results?

The researchers concluded that, “this study demonstrated that a tomato-rich diet is independently related to lower prevalence of depressive symptoms. These results suggest that a tomato-rich diet may have a beneficial effect on the prevention of depressive symptoms. Further studies are needed to confirm these findings.”

Conclusion

This cross-sectional study examined the relationship between the intake of various vegetables and tomato products (a major source of lycopene) and depressive symptoms in elderly Japanese people.

They found a statistically significant trend indicating higher levels of tomato or tomato product were associated with less risk of depressive symptoms.

By contrast, no other vegetable groups were found to be significantly linked with depressive symptoms.

This study had some strengths, including its adequate size and that it adjusted for a large number of variables that may have influenced the link between diet and depression in its analysis. However, there are also some important limitations to consider, including the following points.

Notes:

The type of study

An inherent limitation of cross-sectional studies is that they can only highlight associations between diet and disease – they cannot prove cause and effect, for example, whether eating lots of tomatoes (lycopene) causes fewer signs of depression, or whether people displaying more signs of depression eat less tomato products. Depression and the causes of it are likely to be complex and so there will be many additional factors, outside of antioxidant intake through tomatoes, that influence this relationship and which this type of study cannot account for. If all these factors were adequately accounted for, there may be no link between tomatoes and depression found. Further studies would be needed to see if this is the case.

How depression was assessed

The measure used in the study (the Japanese version of the Geriatric Depression Scale), was just that, a measure of the severity of symptoms of depression. There was no attempt to clinically diagnose depression. So, those reporting mild or severe depressive symptoms may have been a mix of people who had been formally diagnosed with depression and those that hadn’t.

Tomato eating habits were self-reported

The measure of diet was self-assessed by asking people to recall their consumption of various foods from the previous year. This may be prone to significant error in recalling this information accurately which could bias the overall results.

Do Japanese people eat more tomatoes than us?

The majority (56%) of the Japanese participants reported eating tomato products once or more per day, which may be considered a high level of consumption by other countries’ standards. This highlights the fact that diets across the world vary greatly and the results of studies linking diet to disease in other countries are not always directly relevant or applicable to the UK.

High fructose corn sugar causing global diabetes epidemic

“Syrup found in biscuits, ice cream and energy drinks fuelling diabetes on a ‘global scale’,” according to the Daily Mail, highlighting that countries that use large amounts of fructose corn syrup have diabetes rates “20% higher” than countries where it is less used.

 

This report comes from an ecological study looking into whether there is a link between diabetes levels and the availability of high fructose corn syrup (HFCS). Availability is a measurement of how much of a substance is produced or imported into a country – it does not automatically relate to consumption.

HFCS is used as a sweetener in a wide range of processed food and drinks, but its use and consumption varies widely between countries.

The study found that countries that produced and sold the most HFCS also had higher levels of diabetes when compared with countries with the lowest levels of HFCS availability.

Prevalence of diabetes was 8.0% in the countries with high HCFS availability, compared with 6.7% in countries with lower availability – a difference of approximately 20%.

However, this informative study has some limitations and did not set out to prove that high levels of HFCS consumption caused an increased prevalence of diabetes. Importantly, it did not show that the people with diabetes were consuming more HFCS.

Ecological studies such as these are useful but should be interpreted alongside other studies looking into associations between dietary intake (including HFCS), weight and diabetes at an individual level, so that a complete picture of the potential relationships involved can emerge.

Biscuit-loving UK readers of the Mail’s alarming headline will be pleased to hear that consumption of fructose syrup in this country is negligible – a measly 0.38kg per person per year. In the US a whopping 24.78kg per person per year is consumed – more than 65 times that consumed in the UK.

Where did the story come from?

The study was carried out by researchers from the University of Oxford (UK) and the University of Southern California (US). No funding source was reported.

The study was published in the peer-reviewed journal Global Public Health.

Despite a typically arresting headline, the Daily Mail’s reporting of this research is well balanced. Especially useful is the reporting of absolute differences between diabetes rates in the countries: “Rates of diabetes were 8% in high-consuming nations and 6.7% among low consumers – a difference of 20%.”
This is useful for readers to get a feel for the magnitude of the difference being talked about.

 

The usual temptation for media outlets is to only report the headline-grabbing “20% higher” figure without any further explanation, which can leave readers thinking the news is more startling than it actually is.
The Mail should also be praised for including a useful graph that shows readers the sharp differences between HFCS availability in different countries, which is a good visual aid.

What kind of research was this?

This was an ecological study looking at the relationship between the availability of high fructose corn syrup (HFCS) and the prevalence of type 2 diabetes across different countries.

An ecological study is an epidemiological study that analyses data at a population level, rather than at an individual level.

HFCS is a corn syrup modified to increase the level of fructose and is used a lot in some processed foods and beverages as a sweetener to replace sugar, as well as prolong shelf life and appearance.

It is found in a host of items, from soft drinks and breakfast cereals to breads, fast food and yoghurt.

Due to historical and economic reasons – namely a series of US trade tariffs – the use of HFCS is particularly widespread in the US, as it serves as a cheaper substitute for more expensive imported sugar.

The researchers report that a growing body of evidence supports the hypothesis that in addition to overall sugar intake, fructose is especially detrimental to health and increases the risk of type 2 diabetes.

It states that the epidemics of obesity and type 2 diabetes we’re currently seeing constitute an “alarming public health concern”, and that global increases in the use of HFCS in food and beverage production may be contributing to this.

What did the research involve?

Using published resources, the researchers estimated country level estimates of:

  • total sugar availability
  • HFCS availability
  • total calorie availability
  • obesity
  • diabetes prevalence

The information sources used by the researchers included:

  • diabetes prevalence – International Diabetes Federation (IDF), Diabetes Atlas (fourth edition) and global estimates reported by the Global Burden of Metabolic Risk Factors of Chronic Diseases Collaborating Group (GBMRF)
  • food availability – the Food and Agriculture Organization of the United Nations (FAOSTAT) database of 200 countries
  • HFCS production – an international sugar and sweetener report and data on HFCS quotas for EU countries by F.O. Licht, a commercial organisation that provides information and analysis on some aspects of the global commodity market

Information from 43 different countries was analysed, some of which did not use HFCS at all. The researchers then looked for correlations between the dietary elements (total sugar, HFCS and total calories availability) and the rates of obesity and diabetes.

Some of the analysis adjusted for the effects of body mass index (BMI), as well as population and gross domestic product (GDP) obtained from International Monetary Fund (IMF) tables.

What were the basic results?

Data on 43 countries was available covering the use of HFCS (kg per year per person) alongside estimates of total sugar intake (kg per year per person), BMI, and the estimates of diabetes prevalence from two separate sources (IDF versus GBMRF).

Use of high fructose corn syrup per person

 

The US was by far the highest consumer of HFCS out of the 43 nations assessed at 24.78kg per year per person, far ahead of second place Hungary at 16.85kg per year per person. The UK was far lower, at 0.38kg per year per person. Fourteen countries registered 0kg per year per person – all except India were European.

Countries with high HFCS availability versus countries with low HFCS availability
The researchers compared measures from those countries with low availability of HFCS (21 countries) versus high availability of HFCS (21 countries). Countries with high availability were defined as having an average value of more than 0.5kg HFCS per person per year.

The average HFCS consumption in the low-availability countries was 0.1kg per person per year, compared with 5.8kg per person per year in the countries classed as having high availability.

The report stated that all indicators of diabetes were higher in countries that had high availability of HFCS compared with those that had low availability. This trend was more significant for the IDF measure of diabetes prevalence.

Countries with high HFCS availability had an average diabetes prevalence of 7.8%, compared with 6.3% in those with low availability (p=0.013). So, the high-availability countries had approximately 20% higher diabetes prevalence than those with low availability (23.8%)

Using estimates of fasting glucose levels to estimate diabetes prevalence showed the difference was 5.33mmol/L in high HFCS availability countries, versus 5.23mmol/L in low availability countries.

Other influencing factors

There were no significant differences between countries of different availability of HFCS (high versus low) for BMI, total calorie intake, cereal intake, total sugar intake and “other sweeteners” intake.

The researchers interpreted this as meaning that the differences in diabetes prevalence may have had more to do with the level of HFCS availability, rather than these additional factors.

How did the researchers interpret the results?

The researchers concluded that, “Our analysis revealed that countries electing to use HFCS in their food supply have a diabetes prevalence that is ~20% higher than that in countries that do not use HFCS […] even after adjusting for country-level estimates of BMI, population and gross domestic product.”

They linked their own finding to previous research that they reported “showed that increasing consumption of HFCS in the twentieth century was the primary nutritional factor associated with increasing prevalence of type 2 diabetes.”

This led them to warn that, “The increasing popularity of HFCS around the world should, therefore, be considered seriously due to its potential contribution to increases in fructose in the global food supply and its association with the global prevalence of type 2 diabetes.”

They also make the point that even modest increases in disease prevalence can have a significant economic impact if a disease is both common and its treatment complex. They state that the health costs of treating diabetes in the US during 2007 was $174bn. A 20% reduction in diabetes prevalence would save $34.8bn, or approximately $95m per day.

Conclusion

This ecological study suggests that countries with a high availability of high fructose corn syrup (HFCS) – defined as more than 0.5kg per person per year – may have higher diabetes levels than those defined as having low HFCS availability.

Countries where availability was defined as high had approximately 20% higher rates of diabetes than those defined as having low availability.

While informative, this study does not prove cause and effect. For example, this study does not show that individuals with diabetes consumed higher levels of HFCS or that this consumption contributed to their diabetes.

Ecological studies such as these need to be interpreted alongside other studies investigating the association between calorie intake (including from HFCS), weight and diabetes at an individual level, so that the full picture of the relationships involved can be established.

Neither HFCS nor diabetes was measured at an individual level, so we cannot assume that the link reported at the country level would be found if the study used individual level data – for example, examining individual diet and diabetes diagnosis.

The low versus high availability of HFCS cut-offs were not justified for clinical or other reasons in the study, and this may have been an arbitrary cut-off.

The choice of where to put this cut-off for low versus high availability and the reasons for such a decision are very important, as selecting a different cut-off point could lead to vastly difference results.

The precise country level estimates of HFCS and diabetes levels are also likely to be subject to significant error that could affect the results.

However, without assessing each information source in detail we cannot say how important this limitation may be, but it is important to be aware of it.

This type of study design is a useful starting point to identify country level trends, but further research is needed at an individual level to explore whether HFCS consumption is linked to diabetes in any way.

Finally, the fact that HFCS availability was relatively low in the UK would suggest that this is less of a public health issue in the UK than in the USA.
However, consumption of HFCS may vary considerably person to person so the Great British biscuit lover should be aware that eating high levels of sugar (HFCS or otherwise) – or indeed fat – is known to have detrimental effects to health.