People under the age of 55 may be at increased risk of ill health and death if they consume high levels of coffee, researchers have suggested.
The new data has linked consumption of more than 28 cups of coffee a week to an increased risk of mortality in those aged under 55 years - with no adverse effects found in heavy coffee drinkers over 55.
Writing in Mayo Clinic Proceedings, the research team analysed data from more than 40,000 people - finding that more both men and women younger than 55 years of age were linked to more than a 50% increased risk of all-cause mortality.
Led by Dr Junxiu Liu from the University of South Carolina, the research team noted that coffee has long been suspected to contribute to a variety of chronic health conditions - although earlier studies on coffee consumption in relation to deaths from all causes and deaths from coronary heart disease are limited, with often controversial findings.
"In this large US cohort study, a positive association between heavy coffee consumption (>28 cups per week) and all-cause mortality was observed in the total population of men and in men and women younger than 55 years. However, for people 55 years and older, this association was not statistically significant for either sex," wrote Liu and colleagues.
"Hence, it may be appropriate to recommend that younger people, in particular, avoid heavy coffee consumption," they warned - noting that further research is still needed to better assess the effects of long-term coffee consumption and changes in coffee consumption over time on all-cause and cardiovascular disease (CVD) mortality.
The multicenter research team investigated the effect of coffee consumption on death from all causes and deaths from cardiovascular disease in the Aerobics Center Longitudinal Study (ACLS) cohort, with an average follow-up period of 16 years and a relatively large sample size of over 40,000 men and women.
Between 1979 and 1998, nearly 45,000 individuals aged between 20 and 87 years old participated and returned a medical history questionnaire assessing lifestyle habits - including coffee consumption - and personal and family medical history.
Liu and his team examined a total of 43,727 participants in the final analysis with deaths from all causes and deaths from cardiovascular disease identified through the National Death Index or by accessing death certificates.
They found that younger men had a trend towards higher mortality even at lower consumption, but this became significant at about 28 cups per week - where there was a 56% increase in mortality from all causes.
Younger women who consumed more than 28 cups of coffee per week also had a greater than 2-fold higher risk of all-cause mortality than those who did not drink coffee, said Liu and colleagues.
"Significantly, the results did not demonstrate any association between coffee consumption and all-cause mortality among older men and women," noted Dr Steven Blair, senior author of the study.
"It is also important to note that none of the doses of coffee in either men or women whether younger or older had any significant effects on cardiovascular mortality."
The researchers suggested that younger people in particular should avoid heavy coffee consumption of more than 28 cups a week or four cups in a typical day.
However, they emphasised that further studies are needed in different populations to assess details regarding the effects of long-term coffee consumption and changes in coffee consumption over time on all-cause and cardiovascular disease mortality.
Source: Mayo Clinic Proceedings
Published online ahead of print, doi: 10.1016/j.mayocp.2013.06.020
"Association of Coffee Consumption With All-Cause and Cardiovascular Disease Mortality"
Authors: Junxiu Liu, Xuemei Sui, Carl J. Lavie, et al