Effects of Black Currant Anthocyanoside Intake on Dark Adaptation and VDT Work-induced Transient Refractive Alteration in Healthy Humans

Alternative Medicine Review, Dec, 2000 by Hitoshi Nakaishi, Hitoshi Matsumoto, Shigeru Tominaga, Masao Hirayama

Abstract

The effects of oral intake of a black currant anthocyanoside (BCA) concentrate on dark adaptation, video display terminal (VDT) work-induced transient refractive alteration, and subjective asthenopia symptoms (visual fatigue) were examined in a double-blind, placebo-controlled, crossover study with healthy human subjects. In a dark adaptation study, intake of BCA at three dose levels (12.5-, 20-, and 50 mg/subject, n = 12) appeared to bring about dose-dependent lowering of the dark adaptation threshold. Statistical analysis comparing the values before and after intake indicated there was a significant difference at the 50 mg dose (p = 0.011). Comparing the refraction values for the dominant eye, BCA intake (50 mg/subject, n = 21) resulted in no decrease in the average value after the visual task; whereas, a placebo trial resulted in a large decrease in the average value, resulting in borderline significance (p = 0.064). In the assessment of subjective asthenopia symptoms by questionnaire, significant improvement was recognized on the basis of the statements regarding the eye and lower back after BCA intake. (Altern Med Rev 2000;5(6):553-562)

Introduction

In the previous decade, the rapid spread of computers and video display terminals (VDTs) in the home and workplace has led to an increase in ocular and visual problems, including eye discomfort, blurring of distant objects, eye strain, and asthenopia (visual fatigue).[1,2] Regarding nutritional mitigation of visual function problems, several dietary constituents, such as carotenoids,[3] long-chain polyunsaturated fatty acids,[4] and anthocyanosides[5] have been shown to enhance visual acuity. An anthocyanoside complex from bilberry (Vaccinium myrtillus L.) fruits has been reported to enhance visual acuity at night.[6] This effect is reported to be exerted through acceleration of rhodopsin regeneration[7] and/or activation of retinal enzymes.[8] Although the number of scientific reports is few, this information has attracted much :interest in screening anthocyanoside homologues to identify the active compound(s). This information also suggests that intake of anthocyanoside-rich foods may have previously unknown effects in terms of preventing visual problems attributable to working with computers and VDTs.

There are many kinds of anthocyanoside-rich foods and fruits, and the amounts and composition of anthocyanins differ depending on their origin and the preparation process. As the anthocyanoside composition is assumed to play an important role in terms of the physiological activity displayed (such as the French paradox[9] of red wine and antioxidant activity[10]), it is important to evaluate the functions of anthocyanoside preparations with different compositions in order to clarify whether the composition affects physiological activity. Black currant (Ribes nigrum L.) fruits and juice, known to be rich in anthocyanosides, are commonly consumed in many parts of the world.[11] In the present study, a powdered concentrate of BCA was developed from a commercial source,[12] which was found to consist of four anthocyanoside components, having a simple composition compared with bilberry, which has fifteen anthocyanoside components. Its simple composition is assumed to facilitate evaluation of the structure-activity relationship in studies on the physiological activity and bioavailability of the components.

Accommodative alteration or transient myopic shift of refractive status following an extended and/or continuous near visual task is thought to be the most reliable indicator of visual fatigue.[13] However, there have been no reports on the measurement of the alteration or shift after oral intake of anthocyanosides. This paper reports that oral intake of BCA brought about lowering of the dark adaptation threshold in a double-blind, placebo-controlled, crossover study with human subjects, and that the intake of BCA counteracted the transient myopic shift of refractive status after visual tasks such as VDT operation. In addition, assessment utilizing a questionnaire exhibited that BCA intake prevented or improved subjective symptoms of visual fatigue developing after the task.

Methods

Test sample of BCA

A powdered BCA concentrate was prepared from a commercially available black currant juice by the method developed in a previous study.[12] The concentrate contains 9.2-percent BCA, consisting of delphinidin 3-rutinoside (D3R, 4.61%), delphinidin 3-glucoside (D3G, 1.36%), cyanidin 3-rutinoside (C3R, 2.83%), and cyanidin 3-glucoside (C3G, 0.40%), as shown by the HPLC profile in Figure 1. As test samples, capsules were used for the dark adaptation study and juice was used for the transient refractive alteration study. For each study, a placebo was prepared so as to have a taste and color equivalent to those of the test sample. The compositions of the test samples and placebo preparations are shown in Table 1. All other nutrients, reagents, and chemicals used were purchased from commercial sources.