Cardiovascular Risk Factors Maximum in Winter and Lowest in Summer: Study

A large number of people are more likely to succumb to some form of cardiovascular disease during winter than summers.

Studies conducted in the past have documented the growing heart attack rates during the winter months and some call this phenomenon the Christmas coronary. Studies have indicated low temperatures during winters as the main reason for the increase in death rates. Cold climate narrows the arteries and increases the blood pressure, causing greater stress on the heart. During winters there is a lack of vitamin D, which is associated with higher risk of ischemic heart disease.

Adding to this body of evidence, the new study confirms that cardiovascular risk factors are at the peak during winter months and lowest in summer.

For this study, researchers checked whether cardiovascular risk factors have a seasonal pattern that could solve the mystery of seasonality in deaths. To proceed they gathered data from 10 population- based studies from 7 different countries.

The data focused on cardiovascular risk factors in 107,090 subjects aged 35 to 80 years. The study included 21,128 subjects from Belgium, 25,532 from Norway, 9,359 from Russia, 15,664 from Denmark, 18,370 from Italy, 1,626 from France and 15,411 from Switzerland.

The researchers compared the subject's levels of lipids, glucose, blood pressure, body mass index as well as their waist circumference, according to the seasons. After considering factors like age, gender, smoking habit, the data on blood pressure, lipids and glucose were adjusted for BMI and whether the subject was on any medication.

After analyzing the data, the researchers noticed that the levels of several cardiovascular risk factors that included waist circumference, blood pressure and total cholesterol were higher during winter i.e. in the months of January-February and were found to be lower in summer i.e. from June-August.

They also noticed the systolic blood pressure level was on an average 3.5 mmHg lower during the summer months compared to winters.

"Although this difference is almost irrelevant for an individual, it is considerable for a whole population because the whole blood pressure distribution is shifted to higher values, increasing cardiovascular risk. Indeed, the impact of season on blood pressure levels might have as great an impact on cardiovascular risk as genetic markers for blood pressure. This is because the joint effect of genetic markers on blood pressure is modest, between 2 and 3 mmH," Dr Marques-Vidal, the study lead, said in a news release. "We are currently conducting a study involving 50 million deaths in 18 countries to discover whether seasonality of risk factors affects the risk of dying from myocardial infarction or stroke."

The waist circumference during summer remained 1cm smaller on average compared to winters. The total cholesterol was also found to be on average 0.24 mmol/L lower during the summer months.

The researchers noticed a seasonal change in the waist circumference but not in the BMI. The researchers are still trying to find the mystery behind this. They assume that during winter the total cholesterol increases due to the eating habits. The glucose level also didn't change according to season.

Researchers say that during winters people need to make extra effort to stay fit by exercising and eating healthy food as the risk to cardiovascular health is high.