To the best of our knowledge, this is the first study in humans investigating the metabolic effects of dietary administration of rose hip. Daily consumption of rose hip was found to significantly decrease plasma cholesterol and systolic blood pressure in obese, non-diabetic individuals, whereas no effects on body weight, glucose tolerance and markers of inflammation were observed. The reduction in plasma cholesterol and systolic blood pressure was estimated to lower the risk of developing cardiovascular disease by 17%, using the algorithm for Reynolds risk assessment score.
The magnitude of the lowering of plasma levels of LDL cholesterol in the rose hip group, that is 6.0% compared with the control, was within the range from 6 to 15% that has been reported in the few long-term studies performed on cholesterol-lowering effects of single foods16, 17, 18, 19
and accords very well with the 5% reduction considered realistic in real-world situations when dietary saturated fat levels are low.20
The observed decrease in LDL cholesterol in the rose hip group is below the minimum of 8–9% required to see a reduction in total mortality, although it is estimated to reduce the incidence of coronary heart disease by 14.5%.21
With the exception of two individuals who had slightly elevated cholesterol levels, the participants of the present study had normal plasma cholesterol levels. Thus, the full potency of rose hip to lower plasma cholesterol may not have been revealed and a follow-up study in hyperlipidemic individuals seems warranted. Cholesterol-lowering properties of rose hip have previously been demonstrated in a study performed in high-fat diet fed C57BL/6J mice.13
In that study, the reduction in total plasma cholesterol was shown to involve a reduction in both LDL cholesterol and HDL cholesterol with a larger effect on LDL cholesterol, resulting in a decreased LDL/HDL ratio. In the present study, a very similar profile of the cholesterol-lowering effects was observed, with a significant reduction in LDL cholesterol and LDL/HDL ratio, and a smaller, in this case non-significant, lowering of HDL cholesterol. In a previous human study where a rose hip drink was administered daily to hypercholesterolemic subjects for 6 weeks as a control to intake of the same drink supplemented with Lactobacillus plantarum
299v, no cholesterol-lowering effects were observed by rose hip alone.22
The reason for the discrepancy compared with the present study is not known, but it should be pointed out that besides differences in the characteristics of subjects, the dose of rose hip was only about 25% of that employed in the present study. In another study where 5
g of a standardized rose hip powder (Hyben Vital) was administered daily for 3 months to patients with osteoarthritis, total cholesterol was reduced by 8.5%, indicating that lower doses of rose hip may also promote lowering of plasma cholesterol if administered for longer periods.23
It should be pointed out, however, that besides differences in dose and length of administration, also the preparation of rose hip differs between studies, making comparisons difficult. For instance, the powder used by Rein et al.23
contains both the seeds and shells of the rose hip plant, whereas only the shells were used in our study. The fact that the cholesterol-lowering effects were exerted by both of these preparations may indicate that the shells rather than the seeds account for the cholesterol-lowering properties of rose hip.
The mechanism whereby rose hip is capable of reducing plasma cholesterol is unknown. In the study performed in C57BL/6J mice, the reduction in plasma cholesterol was accompanied by reduced levels of hepatic cholesterol, but the expression of SREBP-2 and HMG-CoA reductase was unaltered, indicating that cholesterol biosynthesis was unaffected.13
It is possible that the high fiber content of rose hip impairs the enterohepatic circulation of bile acids by preventing their re-absorption, thereby promoting increased synthesis of bile acids from cholesterol, that is, a mechanism of action similar to that of the cholesterol-lowering drug cholestyramin.
The observed decrease in systolic blood pressure (4
Hg) was close to the median reduction observed in 27 pharmacological trials estimated to result in decreases of the incidence of coronary heart disease and stroke by >15% and 25%, respectively.24
In a previous study, no decrease in blood pressure in smokers was observed by daily intake of rose hip for 6 weeks, whereas intake of the same rose hip drink supplemented by Lactobacillus plantarum
resulted in a significant reduction of systolic blood pressure.25
The dose of rose hip employed was about 25% of the dose in the present study, which may explain why no effects were observed. The mechanism whereby rose hip lowers systolic blood pressure is unknown. As for the cholesterol-lowering effects, it could be speculated that the high fiber content of rose hip at least partially accounts for the effect. Consumption of the rose hip drink corresponded to a daily intake of 31
g of fiber. Two meta-analyses have concluded that an increase in fiber intake of 10–15
g per day for 8 weeks was associated with a decrease in systolic blood pressure of 1–2
Thus, the reduction of 4
Hg in the present study is likely to be a result of the high fiber intake, although it may very well be that other bioactive components than fiber contribute to the blood pressure-lowering effects of rose hip.
Daily intake of rose hip had no effects on body weight or glucose tolerance. This is in contrast to two previous studies performed in mice, where dietary intake of rose hip potently inhibited body-weight gain and also significantly improved glucose tolerance.12, 13
The reason for this discrepancy is not known, but two obvious differences relate to the dose administered and the metabolic status of the study population. Although the daily intake of rose hip powder in the current study was high compared with previous studies in humans (40 vs 5
g8, 11, 23, 28
), it was much lower than that in the study in C57BL/6J mice, where rose hip accounted for 30% of the daily food intake. The fact that the participants of the current study, in contrast to the mouse studies, were on an energy-restricted diet throughout the study could have obscured effects on body weight and future studies in a large number of overweight, or even lean, individuals on a non-restricted diet would be of interest. Also, the present study, designed to represent a first proof-of-concept study of possible metabolic effects of rose hip in humans, was performed in obese individuals with no diabetes and with only a few glucose-intolerant participants. This is in contrast to the high-fat fed C57BL/6J mouse model, where obesity is accompanied by glucose intolerance.
Several previous studies have demonstrated that the dietary administration of rose hip to individuals with osteoarthritis and rheumatoid arthritis exerts anti-inflammatory effects.7, 8, 11, 29
Obesity and its associated diseases are considered to be states of low-grade inflammation. However, we were unable to detect any significant differences with regard to two markers of systemic inflammation, that is, CRP and PAI-I, or with regard to adiponectin, an adipokine with anti-inflammatory as well as insulin-sensitizing effects. Possibly the most obvious explanation for the lack of effect on these markers is that the low inflammatory tonus of our participants, shown by levels of CRP and PAI-I within the normal range, makes it difficult to demonstrate anti-inflammatory actions, at least as effects on these markers of inflammation.
Although the mechanisms whereby rose hip lowers systolic blood pressure and plasma cholesterol levels remain unresolved, the findings of this study may have important health implications. The current study could be the starting point for exploring rose hip as a constituent of food portfolios aimed at reducing cholesterol and blood pressure, and thereby decrease the risk of coronary heart disease and mortality. Efficient food portfolios are urgently needed and they represent an attractive alternative to statin treatment for people that, because of muscle pain and increases in liver and muscle enzymes, do not tolerate statins, as well as for people at risk of developing diabetes, as statins recently were shown to increase the risk of diabetes.30
Food portfolios designed to lower plasma cholesterol typically contain soy, nuts or almonds, viscous fiber and plant sterols.20, 31
It would be of interest to explore the potential additive and synergistic effects of rose hip in such portfolios. Follow-up studies of dietary treatment with rose hip should not only be performed in hyperlipidemic and hypertensive individuals in order to study its potency in lowering cholesterol and blood pressure in more detail, but also in diabetic individuals in order to further explore its possible antidiabetic effects.