“Inter-individual variability in telomere length is highly heritable. However, there has been a resurgence of interest in the controversial relationship between diet and telomere length,” the researchers wrote.
For this study, published in the European Journal of Clinical Nutrition, the scientists looked at how the telomere, “a region of repetitive nucleotide sequences at each end of a eukaryotic chromosome,” responds to an individual’s nutritional intake based on existing scientific literature. It has been postulated that telomeres protect the end of the chromosomes, preventing replication errors during cell division. Loss of telomeres and the resulting imperfectly replicated DNA strands is thought to be one of the mechanisms in the gradual rundown of cellular function that characterizes aging.
There is scientific consensus that telomere length indicates the longevity of a person, the researchers wrote—the longer the telomere length, the longer the lifespan. “Telomeres are subjected to truncation during cell division, so in each duplication, the end of the chromosome is shortened. Besides cell division, it has been reported that the rate of telomere shortening is precipitated by oxidative stress and inflammation,” they explained.
Selecting the studies
Using the databases PubMed, Science Direct, The Cochrane Library, and Google Scholar, they selected studies up to November 2015 that looked for the association of food items and dietary patterns with telomere length.
Excluded studies were ones that were in vitro or animal studies, duplicated publications, review articles, articles assessing this relationship in the nutrient-level including macros- and micronutrients, and ones that analyzed alcohol intake.
Out of a combined 433 articles they found in all databases, 109 were excluded for being duplicates. The next step was to screen titles and abstracts. Excluded from this phase were 267 for having no report on the exposure and outcome of interest, 19 for not being an observational, animal or in vitro design, 1 for observing alcohol intake, and 13 for being review papers.
The remaining was screened as a full text, and in the end, only 17 human studies were included in the final systematic review. All studies combined, the total sample size was 36,886, skewing more towards women with European ancestry though two studies (one conducted in China, and another conducted among multi-ethnic residents in New York) added diversity to the mix.
Many studies looked at healthy middle-aged adults, several looked specifically at an elderly population, one study looked at children and adolescents aged 6 to 18, and several studies looked at a population with diseases, such as gastric cancer or colon cancer.
Is a Mediterranean diet the secret to longevity?
The review yielded inconsistent results, the report said. Based on the 17 studies, “it appears that specific food items including processed meat, cereals, and sugar-sweetened beverages may be associated with shorter [telomere lengths].”
According to the researchers, diets rich in fruits, vegetables and whole grains is associated with lower mortality from chronic diseases and lower concentrations of inflammation biomarkers, therefore “it is hypothesized that dietary components associated with oxidative stress and inflammation may influence on telomere length.
“However, we found limited number of studies with significant results. Of 3 case-control studies, only 1 showed positive association between high intake of fruits and telomere length; others did not confirm any relationship between dietary patterns or food groups and telomere length,” they wrote.
Three of the studies looked at adherence to a Mediterranean diet. Though the study didn’t specify a definition for this dietary pattern, it is popularly understood as “a diet traditionally followed in Greece, Crete, southern France, and parts of Italy that emphasizes fruits and vegetables, nuts, grains, olive oil (as opposed to butter) and grilled or steamed chicken and seafood (as opposed to red meat),” as explained by Medicine Net. The researchers found the Mediterranean dietary pattern was related to longer telomere lengths in all three of the studies reviewed.
Barriers to studying diet and telomere length
“Some possible reasons have been suggested for these conflicting findings—Telomere lenth is under genetic control and shows inter-individual variation beginning at birth,” they wrote.” In addition, studies included in this systematic review were mostly cross-sectional in design; therefore, inherent differences in telomere length were not considered in these studies”
They added: “Additional epidemiological evidence and clinical trials should be considered in future research in order to develop firm conclusions in this regard.”
Source: European Journal of Clinical Nutrition
Published online August 2016, doi: 10.1038/ejcn.2016.149
Author: N. Rafie, S. Golpour Hamedani, F. Barak, S. M. Safavi, and M. Miraghajani