Take Heart: New Research Strengthens the Cardio/Endocrine Connection

The myriad links between the endocrine and cardiovascular systems have been well known by researchers for years. Two international studies further demonstrate this relationship while showing the impacts caused by such diverse factors as air pollution and soy consumption.

According to the Endocrine Society’s Facts and Figures report on Cardiovascular & Lipids, cardiovascular disease is the number one cause of mortality in the U.S. Although the death rate from cardiovascular disease has declined in the 2000s, due in part to improved lipid levels in U.S. adults, more than half of these adults age 20 years and older still have abnormal lipid profiles.

Something in the Air

In “The Association Between Air Pollution Exposure and Glucose and Lipids Levels,” published in The Journal of Clinical Endocrinology & Metabolism, senior author, Victor Novack, MD, PhD, of Soroka University Medical Center and Ben-Gurion University in Beer Sheva, Israel, and team in collaboration with the Harvard School of Public Health pick up the thread started by prior studies exploring the association between exposure to air pollution and increased risk of cardiovascular, respiratory, and metabolic diseases. Particulate matter is especially hazardous in desert areas, such as the Negev region in southern Israel.

“Several studies … have addressed the link between air pollution and heart diseases, but the question whether the exposure to air pollution triggers or causes these events is yet unclear. Further studies are needed in order to address this gap in knowledge.” – Victor Novack, MD, PhD, Soroka University Medical Center and Ben-Gurion University, Beer Sheva, Israel

“The scientific evidence supports a causal association between air pollution and oxidative stress, possibly involving impaired metabolism of glucose and lipids,” Novack says. “In a recent study performed by our group, we observed a significantly increased risk for ischemic stroke among young adults, associated with air pollution exposure. Following these findings, and as a part of the possible theory linking the association between air pollution exposure and cardiovascular diseases, we sought to investigate if this association might be mediated through the well-established cardiovascular risk factors such as abnormal lipid and glucose metabolism.”

In a population-based retrospective cohort study, the team took blood samples from 73,117 adult participants in southern Israel from 2003 to 2012, diagnosed with stroke, ischemic heart disease, dyslipidemia, diabetes, or hypertension or being a known smoker, to assess glucose, low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides, and hemoglobin (Hb)A1c levels.

“We observed significant increases of up to 0.57% in blood glucose, 2.37% in LDL, and 0.31% in triglycerides and a decrease of up to 1.13% in HDL levels associated with increases of interquartile range (IQR) in average concentrations of particulate air pollution <10 µm in the three months preceding the test (IQR = 20 µg/m³),” Nocack explains. “Similar associations were observed with particulate air pollution <2.5 µm.”

Of note, short-term exposures (one – seven days), did not produce similar effects. However, these associations were stronger among patients with diabetes not treated with antidiabetic medications (other than insulin), such as metformin, which seem to protect against the air pollution–induced changes in serum glucose.

“Although the health effects reported in this study are relatively small, these findings are significant in light of the broad extent of exposed population and the continuous nature of exposure,” Novack says.  Although genetics play a major role in the development of diabetes, the link between air pollution exposure and the development of diabetes and diabetes-related deaths has been demonstrated. Maintaining glycemic control and managing glucose values can translate into clinically meaningful variations in cardiovascular disease risk, he explains. Furthermore, regarding lipids, lowering LDL cholesterol even by a very small amount reduces cardiovascular mortality and morbidity (Facts & Figures: Cardiovascular & Lipids reports a 29% lower death rate in the United States since 1999, attributable to lipid-lowering drugs).

“Several studies, similar to our study, have addressed the link between air pollution and heart diseases, but the question whether the exposure to air pollution triggers or causes these events is yet unclear. Further studies are needed in order to address this gap in knowledge,” Novack says.

Heartening News for PCOS Patients

Dyslipidemia also plays a significant role in polycystic ovary syndrome (PCOS), which is also associated with hyperinsulinemia, impaired glucose metabolism, hyperandrogenism, and oxidative stress. Because soy isoflavones have demonstrated protective effects against a variety of conditions, notably, coronary heart disease and hyperlipidemia, in studies in human and animal models, possibly due to the phytoestrogens’ inhibitory activity on estrogen metabolism enzymes and on insulin discharge by the pancreatic islets, a team led by Zatollah Asemi, PhD, of Kashan University of Medical Sciences in Kashan, Iran, used them to determine their effects on the metabolic status of women with PCOS.

“…Women with PCOS who incorporate foods high in soy … in their diets, such as soy milk, soy nuts, and miso soup, could improve both metabolic and cardiovascular health.” – Zatollah Asemi, PhD, Kashan University of Medical Sciences, Kashan, Iran

In “The Effects of Soy Isoflavones on Metabolic Status of Patients with Polycystic Ovary Syndrome,” also published in The Journal of Clinical Endocrinology & Metabolism, the team report on their prospective randomized, double-blind, placebo-controlled clinical trial in which 70 patients with PCOS aged 18–40 years from December 2015 to February 2016 were divided into soy isoflavone supplement or placebo groups. The 35 participants in the supplement group were given 50 mg/d (an amount comparable to 500 mL soy milk) of soy isoflavones comprising 37.5 mg genistein, 10 mg daidzein, and 2.5 mg glycitein for 12 weeks. Participants in both groups were instructed to maintain ordinary physical activity levels, to avoid nutritional supplements, and to keep food records during the trial.

By analyzing blood samples from the two groups, researchers found that participants receiving soy isoflavone supplements had significantly lower serum insulin, testosterone, and very-low-density lipoprotein and triglyceride levels than their counterparts in the placebo group.

“Soy isoflavone administration for 12 weeks in women with PCOS may improve clinical and metabolic signs through decreased markers of insulin resistance; hormonal profiles, especially androgens; and biomarkers of oxidative stress,” Asemi says. “These findings suggest that women with PCOS who incorporate foods high in soy isoflavones in their diets, such as soy milk, soy nuts, and miso soup, could improve both metabolic and cardiovascular health.”

Horvath is a freelance writer based in Baltimore, Md. She wrote about the number of lymph node that need to be removed in order to determine metastases with thyroid cancer in the January issue.