Does creatine supplementation improve the plasma lipid profile in healthy male subjects undergoing aerobic training?

Several recent studies have indicated that creatine (Cr) supplementation may reduce the symptoms and progression of certain diseases, including mitochondrial cytopathies [1], neurodegenerative diseases [2] and glucose intolerance [3]. In addition there is evidence that Cr supplementation may also improve the lipid profile when combined with exercise training. Kreider et al. [4] reported higher plasma HDL-cholesterol levels and lower VLDL-cholesterol in Cr-supplemented athletes undergoing resistance and agility-sprint training compared to their non-supplemented counterparts, while Arciero et al. [5] reported lowered plasma total cholesterol concentrations after 28 days of Cr supplementation combined with resistance training. In contrast, Kreider et al [6] did not observe any changes in the plasma lipid profile of athletes after 21 months of Cr supplementation. However, none of the aforementioned studies were undertaken with the specific intention of examining the changes in plasma lipid profile. The designs of these studies did not allow any conclusion regarding possible additive effects of Cr supplementation on the plasma lipid profile during training.

To our knowledge, only Earnest et al. [7] reported a specific effect of Cr supplementation on the plasma lipid profile. This group observed that physically active subjects with high basal cholesterol levels exhibited a reduction in blood total cholesterol, triglycerides and VLDL-cholesterol, after 12 weeks of Cr supplementation. The authors attributed these changes to a reduction in blood glucose (P = 0.051) brought about by Cr supplementation. Reduced blood glucose was interpreted to indicate an enhancement in insulin sensitivity, which simultaneously could improve the lipid profile if followed by a reduction in fasting insulin levels [7]. It is known from other studies that, changes in glycemia and/or insulinemia may directly affect blood lipoproteins [8–10].

Pedersen and Saltin [11] have reported that aerobic training has a positive effect on blood lipoproteins. Independently, Walsh et al. [12] have indicated in vitro a regulatory effect of creatine (Cr) and phosphorylcreatine (PCr) on oxidative phosphorylation in mitochondria which is consistent with a model first proposed by Wyss et al [13], as well as the boader view that the primary role of the Cr-PCr/CK system is the regulation of ADP homeostasis [14]. These authors demonstrated that PCr decreases the sensitivity of mitochondrial respiration to ADP whereas Cr has the opposite effect [12]. Several investigations have shown increases in Cr content with little or no change in PCr following Cr supplementation [15, 16]. This would lead to a reduced PCr/Cr ratio, favouring an increase in intra-mitochondrial [free ADP]. Walsh et al. [12] noted that a combination of increases in [free ADP] and [Cr] at rest would elevate mitochondrial respiration and oxidative phosphorylation after Cr supplementation. This raises the possibility that Cr supplementation could exert an additive effect to aerobic training on the balance of lipid and carbohydrate utilisation as fuels during training, with long term effects on the blood lipoprotein profile. Theoretically this could provide an explanation for the positive effects observed by Kreider et al. [4], Arciero et al. [5] and Earnest et al. [7] (though we note again that no similar effect was observed by Kreider et al [6]).

We have recently demonstrated that Cr supplementation and aerobic training have an additive effect on glucose tolerance, which could not be attributed to an enhanced training capacity alone [3]. From this we hypothesized that the inclusion of Cr during aerobic training may also affect the plasma lipid profile, particularly in early training. The aim of this study was therefore to test the possible synergistic effects of Cr supplementation and aerobic training on the plasma lipid profile, glucose and insulin levels in healthy, sedentary, males.

Of the 103 people who responded to the initial request for volunteers, 79 were excluded as they performed regular physical activity or expressed self-reported chronic disease. The remaining 24 subjects were randomly assigned to the CR or PL groups. Two subjects were subsequently lost in the PL group: one withdrew for personal reasons and one was excluded because they missed 2 consecutive training sessions. Consequently 12 subjects remained in the Cr group and 10 in the PL group.

Twelve weeks of aerobic training significantly increased the running distance per session (CR: 42.1 ± 6.3% and PL: 36.8 ± 7.9%, P = 0.05 time main effect). There was also reduction in body fat content measured by skinfold thickness (CR: -26.6 ± 3% and PL: -25.9 ± 3.9%, P = 0.04) and resting heart rate (CR: -9.09 ± 2.2% and PL: -8.9 ± 2.8%, P = 0.05).

Despite the high absolute dose of Cr ingested by subjects with the highest body weights (compared with ACSM recommendations in 2000 [25]), there were no reports of any deleterious effects assessed through the subjective questionnaire.

Lipid profile values can be found in Figure 1. There was no significant difference between groups at baseline. However, there were increases in HDL-cholesterol (Post 4 versus Post 8; P = 0.01) and decreases in TAG and VLDL-cholesterol (Pre versus Post 4 and Post 8; P = 0.02 and P = 0.01, respectively) in both groups (main time effect). No variable was significantly changed with Cr supplementation (interaction effect).

As body weights in the CR group ranged from 64.3 to 110.0 kg, absolute doses of Cr given in the first week ranged from 19.3 to 33.0 g·day^-1, with 50% less during the following eleven weeks. The mean body weight of the CR group was 83.1 ± 16.3 kg. The dose of 0.3 g·day^-1·kg ^-1 was chosen to ensure that subjects even at the lowest body weights received a loading dose close to 20 g per day, although the same relative dose resulted in a higher loading dose in subjects at the upper end of the weight range. However, we were cognisant that some authors have suggested that use of a low Cr dose may have been responsible for the lack of change in lipid profile in the study of Volek et al. [18]. The doses of Cr used in this study are comparable to the fixed dose of 20 g·day^-1 used by Arciero et al. [5] during the first 5 days, and 10 g·day^-1 over the next 3 weeks.

Following the earlier work by Earnest et al. [7] our aim was to test if Cr supplementation combined with aerobic training was an effective strategy for the improvement in the lipid profile in healthy sedentary males. The main findings were a reduction in triglycerides and VLDL-cholesterol, and an increase in HDL-cholesterol, after moderate intensity aerobic training (main time effect). However, Cr supplementation had no further effect on lipid profile improvement. It is important to note that we did not test the effect of aerobic training per se on lipid profile. We tested for a possible additive effect of Cr supplementation on the previously described improvement in lipid profile after aerobic training [26, 27].

Our findings do not agree with those of Earnest et al. [7]. The differences between studies may have arisen from differences in their research design. Earnest et al. [7] selected hypercholesterolemic men and women (those with total cholesterol levels higher than 200 mg/dl), while we investigated healthy sedentary males. Thus, it was expected from the outset that a lower adaptative response would be shown by our subjects since their baseline values were within the normal range (see figure 1, baseline data). In addition, Earnest et al. [7] stated that Cr supplementation reduced triglycerides and VLDL-cholesterol levels at week four, and maintained them up to week 12, compared to baseline values (-23%, -22% and -26%, after 4, 8 and 12 weeks, respectively). However, the Cr and placebo groups had different baseline values. Thus, this difference impairs the comparison between groups as is not possible to distinguish between a true treatment effect from a distinct response due to a baseline difference.

Earnest et al. [7] also reported a decreased fasting glucose trend (P = 0.051). According to the authors, such a decrease indicated a possible improvement in insulin sensitivity, which would cause a better lipid profile particularly if followed by a reduction in the fasting insulin levels. However, our results and others [28, 29] have shown neither a significant improvement in insulin sensitivity nor a decrease in fasting glucose, after Cr supplementation. In light of these findings, we may suggest two explanations: 1) Cr supplementation has no effect on insulin sensitivity, or 2) Cr supplementation does improve insulin sensitivity slightly, but not enough to enhance the lipid profile in healthy subjects. As we [3] and others [28, 30] have demonstrated that Cr supplementation may increase both glucose tolerance and glycogen content, we consider the latter hypothesis more plausible. Ferrante et al. [2] indicated that Cr intake can ameliorate hyperglycaemia, typical of transgenic Huntington disease mice, delaying the onset of diabetes. Supporting these findings, Eijnde et al. [31] verified that Cr ingestion can reduce the insulinogenic index in an animal model of inherited type 2 diabetes. Taken together, these results suggest that Cr might exert beneficial effects on glucose uptake mainly in insulin resistant conditions, although the exact mechanisms underlying these adaptations have yet to be clarified. Interestingly, Eijnde et al. [30] showed that Cr intake increases GLUT-4 protein content in line with glycogen accumulation during muscle disuse and a subsequent period of training, suggesting a role of GLUT-4 in Cr-induced glucose uptake enhancement.

Kreider et al. [4] also reported an improvement in the lipid profile of professional football players following Cr supplementation (15.75 g·day ^-1) during 28 days of high intensity training. The supplemented group presented a significant increase in HDL-cholesterol (13%), and a significant decrease in both triglycerides and VLDL-cholesterol (-13%), compared to the placebo group, showing an additive effect of Cr supplementation. Accordingly, Arciero et al. [5] showed that intense strength training in conjunction with Cr supplementation (25 g·day ^-1 for 7 days followed by 5 g·day^-1 for 11 weeks) significantly decreased total cholesterol values (-9.9%) when compared to strength training only. Their results reinforced the hypothesis that Cr supplementation had an additive effect to training effects on the lipid profile. A possible explanation for this phenomenon was that Cr supplementation enhanced training quality indirectly (i.e. by optimizing volume and intensity). In a review manuscript, Durstine et al. [31] suggested that the lipid profile improved incrementally with training volume and intensity. Therefore, as Cr supplementation allowed subjects to train at a higher intensity/volume, then the training itself may have enhanced the effect and not the supplementation per se.

Cr supplementation is reported to be effective mainly in the improvement of performance during sustained or intermittent high intensity exercise and not in aerobic training [25]. Whilst Cr supplementation has not been shown to increase performance in moderate intensity aerobic activity, Walsh et al. [13] have suggested a mechanistic role for Cr in the stimulation of mitochondrial oxidative phosphorylation which clearly could have impact on the relative utilization of carbohydrate and fat as fuel sources, and indirectly could affect the plasma lipid profile. Whilst an attractive hypothesis, our observations do not support any such effect of Cr supplementation.

Volek et al. [18] similarly failed to observe any effect on the lipid profile of three months Cr supplementation and periodized resistance training. Arciero et al. [5] suggested that the lack of change in lipid profile after resistance training in Volek's study might have been a consequence of the low dose of Cr used (5 g·day^-1). However, in our study we provided ~10 g·day^-1 and again no difference between the placebo and the Cr group was observed. Thus, whilst exercise is clearly important in determining the plasma lipid profile, Cr itself does not appear to have any additional effect in healthy males.

Cr supplementation did not have any additive effect on the plasma lipid profile of healthy sedentary males undergoing moderate intensity aerobic training for 3 months. These results may appear contradictory to those of Earnest et al. [7] although we emphasise that this earlier study was carried out on hypercholesterolemic subjects, whereas ours were normocholesterolemic. Notwithstanding the lack of benefits in this present study we would suggest that additional studies should be carried out to investigate any indirect effect of Cr supplementation on the lipid profile as a result of subjects being able to train at a higher intensity.