From Issue Summer 2020
New research from MAFES scientists suggests a new culprit in the development of type 2 diabetes outside of obesity and age: selenium deficiency. MAFES researchers are studying how inadequate amounts of the mineral may impact health.
Dr. Wen-Hsing Cheng, MAFES researcher and food science, nutrition and health promotion professor, has been studying the nutrient for years, specifically the ways in which it interacts with age-related ailments. Cheng's research on nutritional selenium is one of a handful of reputable studies in the world that links the mineral to the quality of aging, where he has shown that it protects against genome integrity in human cells in mice and aids in living a healthier life.
One driver of an accelerated aging process is damage to the ends of chromosomes, or telomere attrition. Chromosomes are threadlike structures in cells that carry genetic information. Over time, chromosome ends naturally wear out and lead to senescence, or loss of the cell's ability to divide and grow. Additionally, when the body is under a great deal of metabolic or environmental stress, the ends of chromosomes are particularly vulnerable to oxidation and premature deterioration.
Maintaining optimized selenium levels through diet is thought to be one factor that may slow cellular damage that accumulates with age, thus circumventing severe and/or earlier-onset osteoporosis, sarcopenia, cataracts, gray hairs, declined wound healing, declined autoimmunity, and, in this study, the onset of type 2 diabetes.
In the process of studying the relationship between type 2 diabetes and selenium, Cheng and his team found a link between the mineral and functionality of the gut's bacterial colony. Cheng explains that, with respect to type 2 diabetes, dietary selenium deficiency reshapes the profile and abundance of gut microbiota, as well as a handful of selenium-dependent proteins known as selenoproteins. Some of these selenoproteins and gut bacteria, in turn, impact the body's glucose metabolism. In individuals with type 2 diabetes, insulin signals are hampered, and blood glucose levels remain, sometimes dangerously high.
Cheng's study focuses specifically on the interplay between suboptimal selenium levels, glucose metabolism, and gut microbiota, and though it is an ongoing study, it is one that shows promise.
"Selenium has many functions, but in the context of type 2 diabetes, we know that it protects against this chronic disease through certain selenoproteins. We're working to identify those proteins, figure out the link between selenium and type 2 diabetes through gut microbiota, and understand the minimum amount of the dietary nutrient required to help prevent the disease in mice. Preclinical testing are commonly performed in mouse models," Cheng said.
Though the well-documented result of extreme deficiency or surplus of selenium is potentially fatal, this study, funded by the National Institutes of Health, is interested in finding the minimum level of selenium required to offset age-related type 2 diabetes. In addition, Cheng is observing the long-term relationship between the disease and the selenium level considered too low to ensure future health.
It is this symptomless middle ground that is most concerning for Cheng.
"When it comes to selenium and in fact, most minerals and vitamins, our body is healthy only at a very small, happy medium. Micronutrients can be something of a double-edged sword at anything other than the appropriate dose of intake," Cheng said.
With this in mind, the temptation for many may be to storm local pharmacies for selenium supplements in hopes of ensuring a graceful, painless aging process, but evidence suggests that high selenium levels as well as low levels have negative effects.
To make these symptomless ailments trickier, despite an estimated 90 to 95 percent of the American population already being at an optimum selenium level, a clinical study published in the 1990s suggested that selenium intakes three- to four-fold higher than nutritional needs could lead to cancer resilience and instilled the belief in the general public that selenium was a mineral of which there was no such thing as "too much." Supplementing and growing selenium-enriched foods quickly became commonplace, but later studies in the 2000s showed that such levels of selenium in the form of selenomethionine could promote type 2 diabetes. Cheng said correcting the misunderstanding about selenium supplementing is an important goal of the study.
"What we need is optimized selenium status in the body. While most of us do not need selenium supplementation, those with suboptimal levels will benefit from it," Cheng explained.
Cheng said Americans get selenium from many sources such as meat, seafood, and Brazil nuts.
"For most of the U.S. population, these sources more than suffice. Supplementing is not a good idea for 95 percent of Americans," he explained.
Cheng added, the challenge rests in knowing who needs to supplement and who doesn't, as suboptimal selenium levels do not display immediate symptoms. The seemingly obvious answer would be to check a person's selenium status with a series of short blood tests. In theory, this would provide information about whether a person is in the estimated five percent for whom supplementation would greatly improve their later quality of life, or if a person could harm their future years by taking too much now. Though it may be a relatively simple blood test to measure selenium, it's a test that is not covered by most insurance policies or rarely recommended by a medical doctor.
Cheng suggests that the best thing to do in the present to promote graceful, painless aging is to strive for healthy eating habits. Whole foods with limited processing and a variety of food choices offer the best possible chance to ensure micronutrient levels, including selenium, that will cause neither immediate complications nor long-term quality of life reductions.
Cheng and his team are conducting their research in hopes that it will make an impact on policymakers.
"Optimal selenium levels keep diabetes and many other diseases in check," Cheng added. "This is good for individuals but also great for policymakers as it provides a cost-effective avenue for managing chronic disease."
With a mass of research acknowledging the public-health challenges of suboptimal selenium levels, Cheng said testing could provide meaningful, positive impacts on people's lives.
This research is funded by the U.S. Department of Health and Human Services' National Institutes of Health. Food science, nutrition and health promotion doctoral student, Ying-Chen "Vicky" Huang, is a new member of the team working on the link between selenium and type 2 diabetes.
Optimal selenium levels keep diabetes and many other diseases in check. This is good for individuals but also great for policymakers as it provides a cost-effective avenue for managing chronic disease.
Dr. Wen-Hsing Cheng
Behind the Science
Education: B.S., Animal Science, National Taiwan University; M.S., Animal Nutrition; Ph.D., Molecular Nutrition, Cornell University
Years At MSU: 7
Focus: Selenium, gut microbiota, and diabetes
Passion At Work: Optimizing body selenium status is cost-effective for healthy aging.