Scientists have linked exposure to light at night with changes in the structure and functioning of the heart

American scientists have discovered a link between exposure to light at night and changes in the structure and function of the heart. Data analysis of more than 11,000 people showed signs of remodeling of several chambers of the heart, and additional monitoring of 73,000 participants revealed an increased risk of heart failure, heart attack, stroke and other cardiovascular disorders. How night lighting can affect the heart is in the "Izvestia" material.

Night light has changed the structure of the heart

Tulane University researchers led by Liu Qi analyzed data from 11,071 participants, 56.6% of whom were women. The average age of the subjects was 61.1 years. At the beginning of the study, the volunteers wore a device with a built-in light sensor on their wrist for seven days, and about three years later underwent MRI of the heart and blood vessels. The results are published in the European Heart Journal (EHJ).

Nighttime exposure to light was considered by scientists to be illumination from three lux or higher during the five-hour period of least activity. The researchers studied the dose-dependent relationship between the amount of light and indicators of cardiac structure and function, taking into account concomitant factors.

People who were exposed to more intense light at night showed signs of concentric hypertrophy of the left ventricle and subclinical deterioration of its function. The height-indexed mass of the left ventricular myocardium was on average 2.4% higher, and the average wall thickness was 1.5%. At the same time, the myocardial contraction fraction was 1.9% lower.

The indicators of left ventricular deformity also worsened: the absolute global circular, radial and longitudinal deformities were lower by 2.7, 2.9 and 2.8%, respectively. The changes also affected other chambers of the heart. Indexed end-diastolic and end-systolic volumes of the right ventricle increased by 0.9 and 1.6%, and the maximum volume of the left atrium increased by 2.3%. At the same time, its emission fraction decreased by 1.1%.

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The disorders were partially associated with reduced sleep

The researchers found a linear dose dependence of all the main identified links.: the higher the exposure to light at night, the more pronounced the adverse changes in heart parameters.

At the same time, a significant part of the found relationships was statistically mediated by sleep duration. It accounted for from 24 to 49% of the effect, depending on the indicator. Thus, shorter sleep could be one of the mechanisms linking nighttime lighting with changes in cardiac structure and function.

The spread of artificial lighting increases the exposure to light at night. Previously, such exposure had already been associated with an increased risk of various cardiovascular diseases, but its possible effect directly on the structure and function of the heart remained poorly understood.

In an additional analysis, the researchers used data from 73,286 people. The relationship between exposure to night light and subsequent cardiovascular diseases and mortality was investigated using proportional hazards models. The follow-up period ranged from eight to 10 years.

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Nighttime lighting has increased the risk of heart disease and stroke

During the follow-up period, people with high exposure to light at night had a 29% higher risk of heart failure than participants without such exposure. In absolute terms, this was 361 versus 218 cases per 100,000 person-years.

The risk of atrial fibrillation with high exposure to night light was 15% higher — 661 versus 520 cases per 100,000 person-years. The probability of myocardial infarction increased by 24% — 302 versus 208 cases, and stroke — by 33%, to 213 versus 152 cases per 100,000 person-years. In addition, participants with high exposure to light at night had a 26% higher risk of death from cardiovascular diseases - 169 versus 104 cases per 100,000 person-years.

Thus, greater exposure to light at night was associated with unfavorable remodeling of several chambers of the heart and subclinical deterioration of their functions. Most of these connections were partially explained by shorter sleep duration.

The authors of the study note that the results obtained help to better understand the possible mechanisms through which night lighting may be associated with an increased risk of cardiovascular diseases and death from them. At the same time, the work shows precisely statistical relationships, and does not prove that night light directly causes the listed violations.