Decreased oxygen levels for a significant period of time during sleep, which is associated with severe sleep apnea, appear to be present in people who smoke, according to a new scientific study – How much does each additional cigarette raise the risk?

Scientists at the Heart Research Institute (HRI) have discovered a link between nicotine levels in the blood and the amount of time people have less oxygen when sleeping.

When a person’s throat and upper airway become partially or totally closed during sleep, breathing ceases for short periods of time.

In a new study published in the journal ESC Heart Failure, HRI researchers discovered that higher nicotine levels were linked to a 2.3-minute increase in time spent with oxygen saturations below 90%.

Time spent with an oxygen saturation of less than 90% is one of the indicators of the severity of sleep apnea.

According to lead researcher Dr. John O’Sullivan of HRI’s Cardiometabolic Disease Group, this indicated that for every cigarette smoked, a person’s oxygen levels were more likely to be “dangerously low.”

“We know smoking is bad for the heart—it’s one of the major risks for heart attacks—and although smoking is known to reduce oxygen concentration in the blood, the interaction of smoking with sleep apnea has not been quantified. Using blood concentrations of the major nicotine metabolite, we were able for the first time to quantify the effect of smoking on oxygen concentrations at night in people with sleep apnea.

“A standardized increase in levels of this metabolite was associated with 2.3 more minutes with an oxygen concentration less than 90 percent in people with sleep apnea. Time with an oxygen concentration less than 90 percent is a proven indicator of bad cardiovascular outcome.”

Sleep apnea and congestive heart failure are common coexisting conditions, but their interaction is unclear, so Dr. O’Sullivan’s team studied hundreds of small molecules called metabolites to figure it out.

“Believe it or not, stiff heart failure—when the heart muscle can still pump blood but is stiff and cannot relax properly—is the most common form of heart failure today and we have almost no treatment options,” said Dr. O’Sullivan.

“We measured molecules in the blood called metabolites and looked at the changes in these metabolites and related these to the severity of sleep apnea.”

As metabolites, which are the building blocks of your metabolism and play an important role in disease, become more widely studied, so too does the area of metabolomics itself. In this situation, the link between sleep apnea and heart failure can be explained by the findings of these studies. The heart uses a variety of metabolites as fuel, and some of these metabolites are also the units of energy that the heart uses.

There were 1,919 participants in the Framingham Heart Study and 1,524 women who were members of the Women’s Health Initiative, both of whom were studied by the researchers.

Despite the fact that sleep apnea affects as many as one in four adults, its long-term effects and connections with other disorders are still a mystery. Almost no research have combined sleep study data with heart failure and metabolomic data from the same people.

Furthermore, new insights into the link between lipid storage, energy storage, and cardiac size and shape were discovered in this work.

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