Bioética, transgenerismo y salud

There have been few longer-term intervention studies into the effects of coffee on glucose metabolism, the majority of which have examined the effects in regular coffee drinkers ^(11–13).

Van Dam, Pasman and Verhoef carried out two trials in coffee drinkers ⁽¹²⁾. In the first, they got participants to drink a litre of filtered CC (made from 70 g of coffee grounds) per day for 4 weeks and compared this to 4 weeks of coffee abstention in a cross-over design. Despite their participants regularly consuming more than 5 cups/day prior to the trial, they still had a large number of dropouts (10/40) due to side effects from the coffee. This is probably due to the very high dose administered or the strength of the drink. The authors reported their dose to be the equivalent of 13 cups of coffee in one litre of liquid. Despite this very high dose they found only a transient effect on fasted glucose: CC tended to increase glucose at 2 weeks (p=0.08) but not after 4 weeks, perhaps indicating a degree of acclimatisation. They did however find CC increased fasted insulin after 4 weeks. Their second study, reported in the same paper, also utilised a crossover design and compared 2 weeks each of filtered CC (52 g in 0.9 l), caffeine (870 mg in six capsules) and placebo (6 cellulose capsules). This study had

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comparable for caffeine, although 870 mg caffeine in 52 g CC, equating to 1.7%

caffeine, would not be unreasonable. In this study they found no effect of either caffeine or CC on fasted glucose, but reported a tendency for higher insulin after both CC and caffeine (p=0.15). They did not report any washout period for either study, either before the studies began or between treatment phases.

In a non-crossover design, Kempf et al. recruited regular coffee drinkers who had an elevated risk of T2DM ⁽¹¹⁾. They were asked to drink no coffee for four weeks, followed by 4 cups of CC/day for another four weeks then 8 cups of CC/day for a final four weeks. Most of their participants were female and obese and had a mean coffee consumption pre-trial of 4 cups/day. They found no effect of CC on either fasted glucose or insulin, nor did they find an effect on 30 min and 2 h glucose and insulin after an OGTT. They did however report that their lower dose of 4 cups/day increased HDL cholesterol and their higher dose of 8 cups/day increased both total and HDL cholesterol with no effect on LDL cholesterol or TAG versus coffee abstention. They also observed a decrease in IL-18, with no effect on IL-6 or CRP. Their lower dose of 4 cups/day was the same as the mean pre-intervention intake of the participants, so it is perhaps surprising that they observed an effect on HDL cholesterol from that dose.

However, their participants underwent a four week caffeine washout prior to the trial, which may be a sufficiently long period of time to reverse any effects of habitual coffee consumption on HDL cholesterol. Unfortunately they did not take any baseline measures before the washout period, so it is not possible to determine whether there was any effect from the washout period.

In a parallel-arm trial, Wedick et al. gave their participants (n=45, across three groups) either 5 cups/day instant CC, 5 cups/day instant DC or control (no coffee) for 8 weeks ⁽¹³⁾. Their participants were overweight (mean BMI = 29.5 kg/m²) regular coffee drinkers (2 or more cups/day). All groups had a 2 week caffeine-free washout period prior to their first visit. Coffees were provided in 2 g portions and participants were instructed to make it up with 177 ml boiling water. This resulted in a reported daily dose of 345 mg caffeine, 302 mg CGA and 78 mg trigonelline in the CC and 216 mg CGA and 65 mg trigonelline in the DC. There were no differences between control and either CC or DC for glucose AUC, 2 h glucose or insulin, nor was there any effect on HDL, LDL or TAG. CC increased adiponectin versus control.

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overweight individuals . In a parallel-arm study, with no control group, their participants were asked to drink at least 3 cups per day of their allotted CC over 12 weeks, after an initial 4 week washout period. They observed a small increase of 0.1%

in HbA1c values for both groups. In the MR group they saw an increase in HDL cholesterol and adiponectin, whereas they saw an increase in TAG and a decrease in systolic blood pressure (SBP) in the DR group. These changes did not remain significant after correction for multiple tests. They found no effect of either coffee on weight, BMI, waist circumference, diastolic blood pressure (DBP), fasted glucose, fasted insulin, HOMA-IR, total and LDL cholesterol.

One study recruited people who were not heavy coffee drinkers (mean consumption:

2 cups/week of coffee and 5 cups/week of tea) and found a reduction in the postprandial glycaemic response following a 16 week coffee intervention ⁽¹¹²⁾. It was a parallel-arm design with a total of 43 participants randomised to one of three treatments: 5 cups/day of instant CC, instant DC or water for 16 weeks. Their participants were overweight Japanese men, aged 40 - 64 y, with elevated fasted glucose. They observed a decrease in AUC glucose and 2 h glucose in both CC and DC groups compared to control, however the results were only statistically significant for the DC group after adjustment for change in waist circumference. They observed no change in insulin in any group.

Effects on blood lipids

In a randomised cross-over study, 20 healthy, habitual coffee drinkers drank 3 - 4 cups of medium roast (MR) or medium light roast (MLR) filtered CC per day for four weeks

(113). Total and LDL cholesterol increased significantly in each group with no difference between groups. HDL cholesterol increased significantly more with MR than with MLR.

They observed no effect on TAG, IL-6 or TNF-. The authors noted that their coffees had higher amounts of cafestol and kahweol than is usually found in paper filtered coffee and hypothesised that this may be the reason for the increase in lipids in their study as these two compounds have been previously identified as lipid-raising ^(114,115). Another randomised parallel-arm trial, over 8 weeks, also found filtered CC raised total, LDL and HDL cholesterol compared to a control ⁽¹¹⁶⁾, although they found the effect only in their highest dose group (720 ml/day), with no effect in a lower dose (360 ml/day) nor in a DC group (720 ml/day).

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control . However, their participants were instructed to drink 3 cups/day of filter CC in the run-in phase, with the active phases being 4-6 cups/day of either boiled CC, filter CC or no coffee for 9 weeks. It is possible that the increase from 3 to 4 - 6 cups/day in the filter CC group was insufficient to produce a noticeable difference in results over this time-frame.

Two meta-analyses have been performed on the effects of coffee on serum lipids, with both finding a dose-response effect of coffee on total and LDL cholesterol and TAG ^(118,119). Both found the effect to be stronger in dyslipidaemic patients and in trials using caffeinated and boiled coffees.