Reply to TMS Wolever

¹ Department of Medical Genetics Ullevål University Hospital Kirkeveien 66 N-0407 Oslo Norway E-mail: benedicte.christensen{at}ioks.uio.no
² Department of Epidemiological Research Institute of General Practice and Community Medicine University of Oslo Oslo Norway
³ Institute of Cardiovascular Research Sahlgrenska University Hospital Gothenburg Sweden

Dear Sir:

Our study, recently published in the Journal, concluded that abstention from filtered coffee reduces the concentrations of plasma homocysteine and serum cholesterol (1). We conducted a randomized prospective intervention study organized as an unblinded controlled trial with the participants randomly assigned to 3 different treatment groups that were to consume for 6 consecutive weeks no coffee, 1–3 cups (175–525 mL) coffee/d, or 4 cups (700 mL) coffee/d. Inclusion criteria were age 24–69 y, a history of daily consumption of coffee for 5 y, and no daily tobacco smoking for the past 6 mo. To assess the coffee–total homocysteine as well as the coffee–total cholesterol association, we controlled for both dietary habits and brewing methods. All participants were asked to follow their usual diet during the trial: the coffee-consuming groups were permitted to drink the type of coffee to which they were accustomed. Before the randomization step, data were recorded on the participants' usual diets (including whether they used milk in their coffee) in the year before entering the trial. After finishing the trial, the participants were asked to report any dietary changes that had taken place during the trial (2). Wolever asks whether the reduction in plasma homocysteine and serum cholesterol concentrations we observed could have been caused by a reduction in milk intake by the group that abstained from coffee.

Before random assignment, 91% of the participants reported that they consumed their coffee black, which agrees with our general impression that most Norwegians prefer black coffee. After finishing the trial, the vast majority of the participants in all groups reported that they had not changed their total intake of milk during the study. Of the 69 participants in the coffee-abstaining group who filled in the questionnaire, 4 (5.8%) reported that they had reduced their intake of milk or dairy products during the trial. Eight of the 69 (11.6%) reported that they had increased their milk intake while abstaining from coffee. In the group that consumed the highest amount of coffee, the corresponding numbers were 4 of 70 (5.7%) reporting a reduction in milk intake and 5 reporting an increase (7.1%). One participant in each of the above groups did not answer this question. Chi-square statistical tests did not show any significant differences between the reported differences in milk intake in the 3 groups.

On the basis of these data, we conclude that reduced milk intake is not likely to explain the observed reduction in plasma homocysteine or serum cholesterol. The observed association is in line with the results of other intervention studies (3,4).

REFERENCES

1. Christensen B, Mosdol A, Retterstol L, Landaas S, Thelle DS. Abstention from filtered coffee reduces the concentrations of plasma homocysteine and serum cholesterol—a randomized controlled trial. Am J Clin Nutr 2001;74:302–7.
2. Mosdøl A, Christensen B, Retterstol L, Thelle DS. Induced changes in coffee consumption alter ad libitum dietary intake and physical activity level Br J Nutr (in press).
3. Grubben MJ, Boers GH, Blom HJ, et al. Unfiltered coffee increases plasma homocysteine concentrations in healthy volunteers: a randomized trial. Am J Clin Nutr 2000;71:480–6.
4. Urgert R, van Vliet T, Zock PL, Katan MB. Heavy coffee consumption and plasma homocysteine: a randomized controlled trial in healthy vounteers. Am J Clin Nutr 2000;725:1107–10.