A study presented at ACC Asia 2024 in Delhi, India, found that consuming over 400 mg of caffeine daily may have increased cardiovascular disease risk in otherwise healthy individuals.

In the cross-sectional study, investigators examined the effects of chronic caffeine consumption on heart rate and blood pressure recovery among 92 normotensive, healthy individuals aged 18 to 45 years. The investigators defined chronic caffeine consumption as intake of caffeinated beverages 5 days per week for over 1 year. The study protocol involved:

• Measurement of baseline blood pressure and pulse
• Three-minute step test
• Postexercise blood pressure and heart rate measurements at 1 and 5 minutes
• Collection of sociodemographic data and daily caffeine intake information.

Caffeinated beverages considered in the study included tea, coffee, and carbonated drinks such as Coca-Cola, Pepsi, Red Bull, Sting, and Monster.

Participant demographics:

• Gender distribution: 55% female, 45% male
• Urban residence: 68%, rural residence: 32%.

Caffeine consumption patterns:

• Mean daily caffeine intake: 320 mg/day
• Median daily caffeine intake: 285 mg/day
• Standard deviation of caffeine intake: 180 mg/day
• Distribution of caffeine sources: coffee: 45%, tea: 30%, carbonated beverages: 15%, energy drinks: 10%.

Caffeine consumption was stratified into the following groups:

• Low: < 200 mg/day (32% of the participants)
• Moderate: 200 to 400 mg/day (48.4% of the participants)
• High: 401 to 600 mg/day (13% of the participants)
• Very high: > 600 mg/day (6.6% of the participants).

For each group, the following data were analyzed:

• Mean resting heart rate (beats/minute)
• Mean resting systolic and diastolic blood pressure (mmHg).

For each caffeine consumption group, the following data were evaluated:

• Mean heart rate immediately postexercise
• Mean systolic and diastolic blood pressure immediately postexercise
• Mean heart rate recovery at 1 minute and 5 minutes postexercise
• Mean blood pressure recovery at 1 minute and 5 minutes postexercise

Among the key findings were:

• 19.6% of the participants consumed more than 400 mg of caffeine daily.
• Chronic high caffeine intake (> 400 mg/day) significantly impacted the autonomic nervous system.
• Consumption of > 600 mg/day was associated with elevated heart rates and blood pressure after exercise.
• The highest caffeine intake was observed in females, business/management professionals, and urban residents.

The investigators found that nearly one-fifth (19.6%) of participants consumed more than 400 mg of caffeine daily, equivalent to approximately 4 cups of coffee, 10 cans of soda, and 2 energy drinks.

The participants with the highest daily caffeine intake (> 600 mg) showed significantly elevated heart rates and blood pressure 5 minutes following completion of the step test compared with those who had lower consumption levels.

Statistical significance:

• P-values for differences in heart rate and blood pressure recovery between caffeine consumption groups were statistically significant (P < .05).
• Confidence intervals for the main findings were reported at 95% confidence intervals (CI).
• Effect sizes (Cohen's d) for the primary outcomes ranged from 0.3 to 0.7.

Multiple linear regression analysis, adjusting for potential confounders such as age, gender, body mass index (BMI), physical activity level, smoking status, and alcohol consumption, showed:

• Adjusted odds ratio for elevated blood pressure in high caffeine consumers (> 400 mg/day) = 1.8 (95% CI = 1.2–2.7)
• Adjusted risk ratio for delayed heart rate recovery in high caffeine consumers = 1.5 (95% CI = 1.1–2.0).

Subgroup analyses:

• Female participants showed a 15% higher sensitivity to caffeine's effects on blood pressure compared with males
• Participants over 35 years old demonstrated a 20% slower caffeine metabolism rate compared with younger participants
• Business professionals consumed an average of 22% more caffeine daily compared with other occupational groups.

Dose-response relationship:

• A linear relationship was observed between caffeine intake and cardiovascular parameters up to 600 mg/day.
• Threshold effect analysis suggested significant changes in cardiovascular parameters became apparent at approximately 350 mg/day of caffeine intake.

Long-term consumption effects and circadian variations:

• Participants reporting chronic high caffeine consumption for > 5 years showed a 25% higher risk of elevated blood pressure compared with those with < 2 years of high consumption.
• Evening caffeine consumption (after 6 PM) was associated with a 30% higher risk of sleep disturbances and elevated nighttime blood pressure compared with morning consumption.

Methodology:

• The 3-minute step test involved stepping up and down a 12-inch platform at a rate of 24 steps per minute.
• Blood pressure was measured using a calibrated oscillometric device (Model XYZ, Manufacturer ABC).
• Heart rate was monitored continuously using a chest strap heart rate monitor (Model 123, Manufacturer DEF).
• Caffeine intake was quantified using a validated food frequency questionnaire specific to caffeinated beverages.

"Regular caffeine consumption could disturb the parasympathetic system, leading to elevated blood pressure and heart rates," stated study author Nency Kagathara, MBBS, of the Department of Internal Medicine at Zydus Medical College and Hospital in Dahod, India.

The investigators suggested that chronic high caffeine intake may have put otherwise healthy individuals at risk for hypertension and other cardiovascular events as a result of its effects on the autonomic nervous system.