Medical Bulletin 12/ June/ 2024

A controlled laboratory experiment involving both healthy adults and adults with coronary artery disease (CAD) found that passive heat exposure significantly increased myocardial blood flow (MBF) in all participants, regardless of age and health status, thereby placing considerable stress on the heart.

The study was published in the journal Annals of Internal Medicine.

Coronary artery disease (CAD) is a leading cause of mortality worldwide, characterized by the narrowing or blockage of coronary arteries due to plaque buildup. This condition restricts blood flow to the heart, increasing the risk of heart attacks. CAD affects millions globally, with rising prevalence due to factors like poor diet, lack of exercise, and smoking.

Recent studies have shown that passive heat exposure, such as from hot environments or certain medical treatments, can significantly increase myocardial blood flow (MBF). Heat exposure can cause significant stress on the heart leading to a supply-demand mismatch in vessels exhibiting flow-limiting disease. With repeated exposures this can result in symptomatic or silent ischemia and increase the risk for adverse cardiovascular events.

In the study, researchers from the Montreal Heart Institute conducted an experimental study comprised of 20 healthy young adults, 21 healthy older adults, and 20 older adults with CAD to quantify the MBF requirements of heat exposure. In a laboratory setting, participants were heated until their core temperature increased 1.5 degrees Celsius (C), and their MBF was measured before exposure and at every increase of 0.5 degrees C to their core temperature.

The result showed that myocardial blood flow increased in all participants when their body temperature increased by 1.5 degrees C. Researchers additionally observed that 7 participants with coronary artery disease experienced asymptomatic heat-induced myocardial ischemia based on imaging evidence.

The findings revealed that heat exposure that increases core temperature by 1.5 °C nearly doubles myocardial blood flow. Changes in myocardial blood flow did not differ by age or presence of coronary artery disease, but some older adults with coronary artery disease may experience asymptomatic myocardial ischemia.

Reference: Hadiatou Barry, Josep Iglesies-Grau, Georgia K. Chaseling, et al. The Effect of Heat Exposure on Myocardial Blood Flow and Cardiovascular Function. Ann Intern Med. [Epub 11 June 2024]. doi:10.7326/M24-3504

New research, published in the journal Obesity, revealed that moderate to vigorous physical activity in the evening for sedentary adults with overweight and obesity is most beneficial in lowering daily blood sugar levels.

Experts explain that it has been well established that moderate to vigorous physical activity enhances glucose homeostasis in adults with overweight and obesity who are at higher risk of developing insulin resistance.

Exercise helps lower blood sugar levels by increasing insulin sensitivity and facilitating glucose uptake by muscles. During physical activity, muscles use glucose as an energy source, reducing the amount of glucose in the bloodstream. This effect continues even after exercising, as the muscles continue to replenish their glycogen stores, further lowering blood sugar levels. Regular exercise also helps maintain a healthy weight and improves overall metabolic health, which is crucial for effective blood sugar management, especially in overweight and obese individuals.

In the study, 186 adults with an average age of 46 years and a body mass index of 32.9 kg/m² participated in a cross-sectional analysis. Researchers monitored the participants' physical activity and glucose patterns over a 14-day period with a continuous glucose-monitoring device.

The volume of moderate to vigorous physical activity accumulated each day was classified into categories: inactive (no activity accumulated), 'morning' (more than 50% of activity between 6 a.m. to noon), 'afternoon' (more than 50% of activity between noon to 6 p.m.), 'evening' (more than 50% of activity between 6 p.m. to midnight), or 'mixed' (no single time window accounted for greater than 50% of the activity).

The results showed that accumulating greater than 50% of moderate to vigorous physical activity in the evening was associated with lowering day, night and overall blood glucose levels compared with being inactive. This association was stronger in those participants with impaired glucose regulation. The pattern of these associations was similar in both men and women.

“Our results highlight the importance of the field of precision exercise prescription. In clinical practice, certified sports and medical personnel should consider the optimal timing of the day to enhance the effectiveness of the exercise and physical activity programs they prescribe,” said Jonatan R. Ruiz, professor of physical activity and health, the University of Granada.

Reference: Clavero-Jimeno, A., et al. (2024) Impact of lifestyle moderate-to-vigorous physical activity timing on glycemic control in sedentary adults with overweight/obesity and metabolic impairments. Obesity. doi.org/10.1002/oby.24063.

After women go through menopause, their risk of heart disease increases dramatically. To improve and support heart and blood vessel health among postmenopausal women, researchers at Penn State studied whether beetroot juice can improve blood vessels function.

The study published in Frontiers in Nutrition indicated that daily consumption of beetroot juice by postmenopausal women may improve blood vessel function enough to reduce future heart disease risk.

Beetroot juice contains high levels of nitrate, which the body converts to nitric oxide. Nitric oxide helps blood vessels expand, making it easier for blood to flow through the circulatory system/ According to the researchers, the ability of nitric oxide to widen blood vessels is known to be particularly helpful during periods of limited blood flow and oxygen delivery, such as during a heart attack.

The study included women considered early postmenopausal, or one to six years post-menopause, and late postmenopausal, six or more years post-menopause.

Participants first had their vascular function tested before consuming two 2.3-ounce bottles of beetroot juice, followed by one bottle each morning for a week. This beetroot juice provided nitrates equivalent to three large beets. After a few weeks, participants drank beetroot juice with the nitrates removed.

Following the final dose, participants underwent another vascular function test. Researchers used an ultrasound to monitor blood flow in the brachial artery before and after a five-minute forearm blood flow restriction. They compared blood vessel expansion when participants consumed nitrate-rich beetroot juice versus the nitrate-free version.

The results indicated that daily consumption of nitrate-rich beetroot juice enhanced blood flow compared to the nitrate-free version. Sustaining this improved blood vessel function over postmenopausal years could significantly lower the risk of heart disease. Furthermore, late postmenopausal women saw the same benefits as the early postmenopausal group.

“Women may need to consume beetroot juice daily — or even more often — to experience all of the potential cardiovascular benefits. Still, this research shows that beetroot juice can be very useful in protecting blood vessel health of mid-life women during a period of accelerating heart disease risk,” said David Proctor, professor of kinesiology and physiology at Penn State.

Reference: Delgado Spicuzza JM, Gosalia J, Zhong L, Bondonno C, Petersen KS, De Souza MJ, Alipour E, Kim-Shapiro DB, Somani YB and Proctor DN (2024) Seven-day dietary nitrate supplementation clinically significantly improves basal macrovascular function in postmenopausal women: a randomized, placebo-controlled, double-blind, crossover clinical trial. Front. Nutr. 11:1359671. doi: 10.3389/fnut.2024.1359671