Friday November 19 2010
Tomatoes have especially high levels of lycopene
“Two glasses of tomato juice a day strengthens bones and can ward off osteoporosis,” The Daily Telegraph reported. It said scientists have found that an ingredient in the drink, called lycopene, slows down the breakdown of bone cells, protecting against the disease.
This news story is based on a small pilot study that compared the effects of lycopene supplements and tomato juice on chemical signs of bone loss in postmenopausal women. Women taking lycopene from either juice or pills had lower levels of the chemical by-product associated with osteoporosis.
The findings of this study highlight an avenue for further research. However, it is too soon to conclude that tomato juice will help fight bone disease. The researchers, though optimistic, make it clear that their study is a pilot and that larger studies that measure actual bone loss or fractures, rather than the signs of the disease, will provide better evidence.
Where did the story come from?
The study was carried out by researchers from St Michael's Hospital in Toronto and the University of Toronto, Canada.
The study was funded by tomato juice manufacturers, the makers of the lycopene supplements and various other organisations. These included the Canadian Institutes of Health Research, the research and development departments of Genuine Health Inc., the HJ Heniz Co, Millennium Biologix Inc., Kagome Co (Japan) and LycoRed Ltd (Israel).
The study was published in the peer-reviewed medical journal Osteoporosis International.
The Telegraph covered the research well, although it is important to highlight some of the study's shortcomings including its small size and the fact that it measured a surrogate marker of bone loss, rather than actual bone loss or fractures.
What kind of research was this?
This small randomised controlled trial investigated whether levels of a substance called N-telopeptide, a marker of bone loss, in the body could be affected by lycopene supplementation in pill form and from tomato juice. Lycopene is a type of antioxidant. It is found in fruit and levels of lycopene are especially high in tomatoes. Antioxidants in general are thought to help prevent damage to cells by neutralising substances called “reactive oxygen species” (ROS), which are by-products of the metabolic process (how the body breaks down food).
The researchers enrolled early postmenopausal women, aged 50 to 60 years old. Women at this age lose bone at an accelerated rate and, according to the researchers, some studies have shown that the rate of bone loss and damage to bone cells is increased by rising levels of ROS.
In this study, the researchers wanted to see whether lycopene supplementation would reduce evidence of bone loss in women at high risk.
What did the research involve?
The researchers enrolled 60 women who had been postmenopausal for at least a year and who were aged between 50 and 60 years. Women were excluded if they were smokers or if they were taking any medications that might affect their bone metabolism or have antioxidant properties (for example, treatments for heart disease, high blood pressure or diabetes). They were asked not to consume any vitamins that may contain antioxidants or foods containing lycopene, such as grapefruit and watermelon, for the duration of the study.
The women were randomly allocated to one of four groups: 15mg of lycopene from regular tomato juice, 35mg of lycopene from lycopene-rich tomato juice, 15mg of lycopene from a capsule, and a placebo capsule containing no lycopene.
All the women were asked to refrain from eating foods that contained lycopene for one month before the start of the study. Height, weight, blood pressure and a blood sample for analysis were also taken before the study started.
The women took the supplement twice a day with meals. Further blood samples were taken for analysis after two and four months of supplementation. The women kept a daily food diary to record the other food and drinks they consumed in the seven days before a blood test. The study lasted for four months. The researchers were mainly interested in blood levels of the substance N-telopeptide. This is one of several substances whose concentration in the blood will increase if bone is being broken down. The researchers also measured a number of other substances in the blood including proteins and enzymes, and also tested blood samples for antioxidant capacity.
The researchers compared the levels of N-telopeptide in the three lycopene supplementation groups with those in the placebo group. They also merged the three lycopene supplementation groups into one group to compare it separately against placebo. This was the main analysis they presented. The analyses were adjusted for factors that might affect the relationship between lycopene and bone health, such as BMI, age, blood pressure, years since menopause and levels of antioxidants and bone-loss markers at the start of the study.
What were the basic results?
The total amount of lycopene absorbed by the body was the same for both women taking supplements and those taking tomato juice. As expected, women taking supplements had more lycopene in their blood than those on placebo at the two- and four-month follow-ups.
After two months, blood levels of N-telopeptide were reduced in the supplementation group, while the placebo group showed increased levels. This difference between the treatment and placebo groups was significant and present at four months. The blood levels of other substances also increased, such as beta-carotene (a pro-vitamin also found in tomato juice and a product of lycopene metabolism).
How did the researchers interpret the results?
The researchers concluded that the levels of reduction in N-telopeptide in the groups receiving lycopene are comparable to those seen in postmenopausal women who are supplemented with calcium and vitamin D, both of which are recommended for preventing osteoporosis.
This was a small randomised controlled trial which the researchers themselves called a pilot study. It provides preliminary evidence of an effect, but must be followed by larger, more robust studies that have clinically meaningful outcomes.
The researchers delivered an in-depth and insightful report of their research, highlighting the main shortcomings of their study. While they are optimistic about their findings, reporting that the size of the reduction in N-telopeptide was similar to that seen as a result of calcium and vitamin D supplementation, they admit that they did not measure bone mineral density (BMD) or follow the participants for long enough to observe any significant changes in BMD.
This means we do not know what effect the reduction in N-telopeptide has on BMD or other outcomes such as fracture rates, which are the important clinical outcomes for women at risk of osteoporosis. As such, the research does not provide evidence that lycopene has a clinically important benefit for postmenopausal women. Longer studies would be needed to determine whether lycopene has a role in preventing osteoporosis.
Importantly, giving the women supplements with greater concentrations of lycopene did not affect the total amount absorbed by the body. This suggests that the body may only absorb what it needs and does not take in more simply because it is given more.
The relationship between beta-carotene and lycopene may also need further research, as it is not clear which of these antioxidants (or both) might be responsible for the changes seen. The potential harms of taking too much of either substance need further investigation.