Clinical trials with blackcurrants
improves eye function and recovery
A.) The eye takes approximately 30 minutes to fully adapt from bright sunlight to complete darkness and becomes one million times more sensitive than at full daylight.
- Subjects in the trial consumed the equivalent of one tablespoon of blackcurrant berries or less.
- The results showed that dark adaptation was significantly improved at the highest level of 50 mg anthocyanin, and two hours after consumption.
B.) The same dose of blackcurrants was shown to greatly reduce visual fatigue following prolonged visual display terminal (computer screen) work 2 hours after consumption. The subject group that did not consume blackcurrants showed a significant deterioration in refractive index indicating visual fatigue, while those who consumed blackcurrants did not show these symptoms.
After two hours of computer work, overall tiredness of the study subjects is less for the subjects who have taken blackcurrant, compared to those who have not. Particularly with eyes and lower back, the difference between the blackcurrant group and the placebo group are significant.
AIDS THE TREATMENT OF GLAUCOMA
Four clinical trials have studied the effects of blackcurrants on the disease of the eye called glaucoma, which is a major cause of visual field defects and blindness. Glaucoma is a disease of the major nerve of vision, the optic nerve. These studies conclude that blackcurrant anthocyanins may be a promising supplement for patients with glaucoma, in addition to anti-glaucoma medication.
A.) The first study looked at the effects of blackcurrant anthocyanins on blood flow in the retina of patients with Normal Tension Glaucoma. Glaucoma is usually associated with high intraocular (eye) pressure. In Normal Tension Glaucoma the intraocular pressure is normal. After consuming 50mg of blackcurrant anthocyanins per day for six months:
- The subjects showed significantly increased blood flows at key sites in the eye.
- No significant changes in blood pressure or intraocular pressure were measured.
- None of the subjects showed progression of their visual field defects.
B.) The second study examined the effect of blackcurrant anthocyanins on the visual field changes with Open Angle Glaucoma patients. After two years of consuming 50mg per day of blackcurrant anthocyanins or a placebo, the results showed that:
- The placebo group had significant visual field mean deviation from the baseline. However, the group taking blackcurrant anthocyanins showed no changes in visual field mean deviation.
- Ocular blood flow in the group taking the blackcurrant anthocyanins increased, but the group taking the placebo, showed no change in ocular blood flow.
C.)The third study examined the effect of blackcurrant anthocyanins on intraocular pressure in healthy people and patients with glaucoma. Elevated intraocular pressure (IOP) is generally recognised as the most important risk factor for glaucoma.The results showed:
- A decrease in the IOP at 2 weeks and 4 weeks from the baseline, in healthy subjects consuming 50mg per day of blackcurrant anthocyanins. This decrease was not observed in the placebo group.
- A decrease in IOP in the glaucoma patients taking blackcurrant anthocyanins compared to the placebo group.
- Changes of visual field deterioration were significantly less in glaucoma patients consuming blackcurrant anthocyanins at 12 months and 18 months after the baseline.
D.) The fourth study aimed to discover the underlying mechanisms that gave the results shown in the study B.) above. i.e. Blackcurrant anthocyanins slowed down the visual field deterioration and elevation of ocular blood flow of open-angle glaucoma (OAG).
Serum (blood) biomarker ET-1 has been implicated in several ocular diseases including glaucoma. After consuming blackcurrant anthocyanins, serum ET-1 concentrations increased to the levels of those in healthy volunteers during the 24-month period. In contrast, those of placebo- glaucoma patients remained at lower levels.
The results of this study suggest that blackcurrant anthocyanins caused normalisation of serum ET-1 biomarker, which may improve ET-1 dependent regulation of ocular blood circulation.
1. Nakaishi, H., Matsumoto, H., Tominaga, S., Hirayama, M. Effects of blackcurrant anthocyanoside intake on dark adaptation and VDT work induced transient refractive alteration in healthy humans. ALTERNATIVE MEDICINE REVIEW 2000, 5: 553-562
2.Ikuyo Ohguroll, Hiroshi Ohgurol, Mitsuru Nakazawa Effects of anthocyanins in black currant on retinal blood flow circulation of patients with normal tension glaucoma. A pilot study. HIROSAKI MEDICAL ]OURNAL. 59: 23-32. 2007
3.Hiroshi Ohguru, Ikuyo Ohguro, Maki Katai, Sachie Tanaka Two-year Randomized, Placebo Controlled Study of Blackcurrant Anthocyanins on Visual Field in Glaucoma. OPHTHALMOLOGICA 2012, 228:26-35
4.Hiroshi Ohguru, Ikuyo Ohguro, Saeko Yagi Effects of Blackcurrant Anthocyanins on Intraocular Pressure in Healthy Volunteers and Patients with Glaucoma. JOURNAL OF OCULAR PHARMACOLOGY AND THERAPEUTICS 2013, Vol 29 No.1:61-67
5. Kaori Yoshida, Ikuyo Ohguro, Hiroshi Ohguru, Blackcurrant Anthocyanins Normalized Abnormal Levels of Serum Concentrations of Endothelin - 1 in Patients with Glaucoma. JOURNAL OF OCULAR PHARMACOLOGY AND THERAPEUTICS 2013, Vol 29, No. 5:480-487.