Can tomato juice protect against cardiovascular disease?
Cardiovascular diseases are responsible for the most deaths in the United States.
People can modify certain risk factors, such as smoking, but it is impossible to modify others, such as age.
So, as the population ages, finding ways of reducing cardiovascular risk is of growing importance.
Nutrition is vital for good health, and heart health is no exception. Now, one new study has asked whether regular consumption of unsalted tomato juice might be a cost-effective intervention.
The study authors explain how the tomato "contains a variety of bioactive compounds, such as carotenoid, vitamin A, calcium, and gamma‐aminobutyric acid, which may play a role in maintaining physical and psychological health, including the prevention of [cardiovascular disease]."
Atherosclerosis in brief
The main driver of cardiovascular disease is atherosclerosis, which occurs when plaque builds up within blood vessels. As time goes on, plaque becomes harder, narrowing the arteries.
Atherosclerosis begins when the endothelium, or the inside surface of blood vessels, sustains damage.
This damage can occur for a number of reasons, some of which are high blood pressure, diabetes, and levels of cholesterol in the blood. If a person can control these three factors, they could significantly reduce their risk of atherosclerosis and other cardiovascular conditions.
The authors of the recent study published a similar study in 2015. In their previous work, they concluded that drinking unsalted tomato juice over 8 weeks reduced the levels of triglycerides in the blood of middle-aged women. Triglycerides are a type of fat; high levels of these fats contribute to atherosclerosis.
Another look at tomato juice
Their previous results prompted the scientists to widen their net and assess whether tomato juice might also benefit other cardiovascular risk factors, such as high blood pressure and lipid and glucose metabolism, over a longer period.
This time, they also wanted to measure the benefits of tomato juice in people of different ages and sexes. The scientists published their findings in the journal Food Science & Nutrition.
According to its authors, "the current study is the first to investigate the effects of tomato or tomato product intake on cardiovascular disease risk markers over the course of a year and over a wide age range."
At this point, it is important to note that the authors received a research grant from the Kikkoman Corporation to conduct both this study and the previous one.
The Kikkoman Corporation manufacture a range of soy sauces but also hold the exclusive marketing rights to the Del Monte brand in Asia, where the company "manufactures and markets tomato-based goods."
1 cup each day
In total, the scientists recruited 184 men and 297 women as participants. For 1 year, all participants had access to as much unsalted tomato juice as they wanted; the average was around 215 milliliters per day per person, which is slightly less than 1 cup.
At the beginning and end of the study, the scientists measured a range of factors, including blood pressure, levels of triglycerides and cholesterol in the blood, and fasting plasma glucose.
They analyzed data from the 94 participants who had hypertension or prehypertension (elevated blood pressure not high enough for the person to receive a diagnosis of hypertension).
Their blood pressure was significantly lower after 1 year of consuming tomato juice. Average systolic blood pressure dropped from 141.2 to 137.0 millimeters of mercury (mm Hg). Also, average diastolic blood pressure dropped from 83.3 to 80.9 mm Hg.
According to the American Heart Association's (AHA) guidelines, this change in blood pressure would move the average participant from hypertension stage 2 down to hypertension stage 1.
These effects were similar for both men and women and people of all ages.
No change for glucose or triglycerides
The researchers also assessed glucose metabolism in 62 participants with untreated impaired glucose tolerance; however, there were no significant improvements for these people.
In a subgroup of 127 participants with abnormal lipid levels in their blood, there were no changes to triglycerides or high-density lipoprotein (HDL), or "good," cholesterol.
However, they did see a significant drop in the level of low-density lipoprotein (LDL), or "bad," cholesterol. LDL is a risk factor for atherosclerosis.
Importantly, using a questionnaire, the researchers ensured that the participants' lifestyles had not changed significantly over the year, which might account for these beneficial changes.
The study has a number of significant limitations; aside from the source of its funding, the study only recruited a relatively small number of participants. In the blood pressure analysis group specifically, there were only 94 individuals.
It is also worth noting that the participants were all residents of Kuriyama, Japan. Therefore, it is possible that the results might not apply to other populations or ethnicities.
Also, the researchers did not have access to the participants' other dietary habits; in some cases, it might be possible that when a participant introduced a glass of tomato juice, it replaced a less healthful snack.
Therefore, it could be the removal of the snack that generated the health benefits, rather than the juice itself.
Also, when the scientists checked for lifestyle changes between the beginning and end of the study, only around half of the participants had completed the questionnaire. It is quite possible that during those 12 months, some people made significant changes to their levels of exercise or food intake.
"The available evidence on the effects of tomato products [on cardiovascular] risk factors supports the view that increasing the intake of these has positive effects on blood lipids, blood pressure, and endothelial function."
The cardiovascular benefits of tomato juice are gathering evidence. However, the new study is not powerful enough to prompt a change in drinking habits; we may need to wait a little longer before we can draw reliable conclusions.