Lipid Profile – One trial recruited adults with elevated or normal cholesterol levels and allocated them to drink either 750ml daily of orange juice from concentrate (i.e. no added sugar) for 60 days versus a ‘no juice’ control.
Amongst those with elevated cholesterol levels at baseline, low density lipoprotein cholesterol (LDL-c) was significantly reduced by the end of the trial, while high density lipoprotein cholesterol (HDL-c) was raised– findings suggesting that orange juice may facilitate free-cholesterol transfer to HDL-c.
Other work on HDL-c has produced similar results. Twenty-five healthy Canadian men and women with elevated total cholesterol levels were allocated to drink 1, 2 or 3 cups (250ml) of 100% orange juice daily over three 4-week periods followed by a 5-week washout where no juice was consumed.
Drinking 750ml juice daily, but not 250ml or 500ml, significantly increased HDL-c by 21% by the end of the trial (Figure 1) indicating that this could be of benefit to those with raised cholesterol levels.
Orange juice may also influence lipid levels in active populations. In one study, 13 women drank 500ml orange juice daily and participated in 1 hour of aerobic training 3 times weekly over 3 months. Their LDL-c levels significantly reduced by 15% whilst HDL-c increased by 18%. No significant changes were noted in the control group.
Interestingly, in the orange juice group only, blood lactate levels reduced and physical performance improved. High blood lactate is a common cause of exercise cramps and muscle soreness.
Mechanisms – In terms of potential mechanisms, cardiovascular benefits may relate to the high hesperidin content of citrus fruits. Hesperidin is a flavone mostly found in orange and lemon.
A French RCT recruited 24 overweight men and randomised them to drink 500ml orange juice, a control drink with hesperidin, or a placebo drink over 4 weeks. The results showed that both orange juice and hesperidin significantly reduced diastolic blood pressure and improved endothelium-dependent microvascular reactivity (an indicator of how well the lining of blood vessels constrict or relax). This suggests that the vascular benefits of oranges and 100% orange juice are probably due to hesperidin.
Similarly, another French trial found that the consumption of blond (yellow) orange juice (up to 600ml daily) over 4 weeks significantly increased antioxidant levels. This, in turn, correlated to hesperitin plasma levels and a reduction in harmful reactive oxygen species.
Other work has found that orange juice consumption can lead to the short-term elevation of 8 different flavanones and 15 phenolic compounds. Flavanones are soluble compounds which are found in the juice cloud, rather than in cell walls which explains their increased bioavailability in juice compared with whole fruits.
It is thought that drinking mixtures of juices could help with aspects of the cardiovascular system by providing an array of polyphenols and vitamins which have their own biological effects.