Previously studies on adults suggested consumption of as little as 1-3 mg/kg of caffeine - at low to moderate levels - was enough to increase blood pressure and lower heart rate, however evidence of its effects on children was inconsistent, said the report on cardiovascular responses.
“Caffeine use among children is increasing and little research has been done to understand the effects of caffeine in this population,” associate professor at the University of Buffalo, Jennifer Temple, said.
“It is critical that we understand how caffeine affects children so that we can develop evidence-based recommendations for caffeine consumption.”
This latest US study analysed the effects of caffeine on children as young as eight years old, and found that doses of one to two mg/kg reduced subjects’ heart rates and increased blood pressure, compared with the placebo.
“We found changes in cardiovascular response with doses as low as 33 mg, which is less than a can of soda. The heart rate changes were between three and eight beats per minute and the blood pressure changes were between one and two mmHg [milimeters of mercury- a unit pressure measurement],” explained Temple.
Gender differences noted
On average, post-pubertal participants consumed more soda, coffee and energy drinks than younger participants, particularly males, and consequently their behavioural and physical reactions were more pronounced, the researchers said.
Responses to a behavioural check list discovered changes in subjects’ energy levels and motivation and physical reactions were also noted, such as queasiness, sweatiness and tiredness.
The scientists observed clear gender differences in heart rate for post-pubertal subjects but none in the pre-pubertal group. This was attributed to the varying effects of caffeine on female subjects at different stages of the menstrual cycle.
The effects of caffeine on post-pubertal girls were particularly prominent during the mid-luteal phase of their menstrual cycle which induced a much lower heart rate and increased systolic blood pressure in the follicular phase, they wrote.
“We are not sure why, but we hypothesise that it is related to changes in steroid hormones that emerge after puberty,” Temple said.
The 96 participants consisted of 26 males and 24 females aged eight to nine years old and 26 males and 20 females aged 15-17.
Subjects were primarily white, middle class and well-educated. They were non-smokers, had already consumed products containing caffeine and suffered no adverse effects, and were not taking any hormone-related medication.
Participants consumed a caffeine solution under laboratory conditions on six occasions over two weeks. For girls aged 15 to 17 three sessions took place during the mid-follicular phase of the menstrual cycle and three during the mid-luteal phase.
Responses were analysed using a behavioural checklist, over a 24-hour period involving food recall and physical exercise activities, and with saliva samples.
Published online ahead of print, doi: 10.1542/peds.2013-3962
"Cardiovascular Responses to Caffeine by Gender and Pubertal Stage"
Authors : J. L. Temple, A. M. Ziegler, A. Graczyk, A. Bendlin, T. Sion and K. Vattanaa