Wilhelmina Kalt obtained her Ph.D. degree from North Carolina State University and is currently employed with the Canadian federal agriculture department, Agriculture and Agri-Food Canada in the province of Nova Scotia.
Dr. Kalt’s research on the health benefits of berries has focused on the anthocyanins of blueberry species and other berry crops. She’s characterized the impact of horticulture and food factors on the antioxidant phenolics in berries and continues to work on the separation of berry phenolic mixtures for use in vitro and in vivo.
Dr. Kalt has conducted animal and human studies to assess the bioavailability and functional bioactivity of blueberry flavonoids, with particular emphasis in vision physiology.
Dr. Kalt is currently the P.I. on a 3 year multi-site initiative than encompasses research in diabetes, vision and cardiovascular disease. One of her specific goals in this work is to develop tools and information for human clinical research using blueberries.
She works closely with industry groups and in particular the blueberry industries, to support the development of their health sector.
Research on Blueberry Anthocyanins and Vision
Kalt, W,1 Fillmore, SAE1, McDonald, J1, Tremblay, FT2.
1Agriculture and Agri-food Canada, 32 Main St. Kentville Nova Scotia Canada B4N 1J5 ; 2 Dept. Ophthalmology & Visual Sciences, Dalhousie University and IWK Health Center, 5850 University Ave., Halifax Nova Scotia Canada B3K 6R8
European research conducted between roughly the 1960’s and 1980’s suggested that bilberry (Vaccinium myrtillus L.) anthocyanins (ACN) benefit vision physiology, particularly under conditions of reduced light (Kalt and Dufour, 1997). However in a review of clinical research, Canter and Ernst (2004) concluded that rigorous placebo-controlled trials did not support a beneficial role for bilberry ACN in night vision. Of the 30 clinical trials conducted, the authors cite 12 that were placebo-controlled, of which four used a randomized controlled (RC) design and reported a negative outcome. A fifth RC trial and 7 non-RC trials reported positive results in outcome measures relevant to night vision. Negative outcomes in clinical trials were associated with more rigorous methodology and lower ACN dosages.
Results of a randomized placebo-controlled, double-blind, cross-over trial that examined the effects of highbush blueberry (BB) juice consumption on human vision under reduced light was conducted. Healthy well-nourished subjects (n=59) were randomized based on age and gender. BB juice (BBJ) was produced from a 50/50 blend of TifBlue and Rubel that delivered to the subjects 250 mg cyanidin-3-glucoside equivalents per day. BBJ or placebo was consumed by the subjects for a period of 12 weeks. Each of the two dietary interventions was followed by an 8 week washout period. Subjects had their vision tested at prescribed intervals as follows. (1) At the start of the study three vision testing sessions were conducted to train subjects. (2) During the intervention, vision was tested at 8 and 12 weeks. (3) During the washout vision tests were conducted at 6 and 8 weeks. Each subject took a total of 11 tests, each of which took about 45 min and included dark adaptometry plus 5 other tests of functional vision once subjects were dark adapted.
PC-based tests were designed to determine: (1) the subject’s rate of dark adaptation, (2) their dark-adapted visual acuity, (3) their dark-adapted contrast sensitivity and (4) their rate of recovery of visual acuity after exposure to bright light (macular stress). Data were analyzed by Genstat (Payne, 2004). Covariate adjustment was applied, based on (1) results of the third pretest (2) first cross-over results and (3) testing sites (1 of 2).
PC-based tests were sufficiently sensitive to detect age-related differences among the treatment groups. However no difference related to the consumption of BBJ was detected in the rate that subjects became dark adapted or their final dark threshold once fully adapted. Also no BBJ-related difference was detected in subject’s dark adapted visual acuity or contrast sensitivity. However BBJ consumption significantly reduced the time needed to recover visual acuity after exposure to bright light (i.e. macular (retinal) stress) (P<0.001, for the mean of 8 and 12 weeks). This BBJ-related reduction in recovery time persisted after 4 weeks of washout (P=0.018) but was absent after 8 weeks.
In a second and similar clinical trial (n=64) which tested dark vision after only a 3 week intervention, BBJ similarly reduced recovery times after macular stress (P=0.012). The results showed that BBJ consumption for as little as 3 weeks can significantly improve one’s ability to regain normal vision after exposure to bright light, with no effect on other parameters related to dark vision. BBJ consumption may benefit individuals who must function in situations of darkness with interruptions by bright light (e.g. drivers, pilots).
The macula, the central portion of the retina, is the region most important in vision. The retina contains abundant photoreceptors that transform light into electrical signals leading to visual perception. Recovery time from illumination stress to the macula (i.e. simulated in the previously-mentioned macular stress test) is related to the photoreceptor’s capacity to regenerate photopigment. The photoreceptor primarily involved in vision under low light is rhodopsin. Matsumoto et al. (2003) reported that black currant anthocyanins, and specifically cyanidin-3-glucoside, stimulated the regeneration of rhodopsin in vitro.
Photoreceptor cells are highly metabolically active and vulnerable to oxidative, mechanical and dys-metabolic stresses. Recovery from retinal stress is related to the health of the photoreceptors therefore it would be interesting to examine the effects of BB in subjects with photoreceptor diseases such as retinitis pigmentosa or age-related macular degeneration. A model useful for examining in vivo BB anthocyanin effects in retinal photostress is light-induced retinopathy (LIR) in rats. In this model a prescribed exposure to bright light leads to measurable apoptosis in photoreceptors after a matter of hours, with more damage occurring over days and leading over a longer period to retinal remodeling. One way to measure damage arising from LIR is with electroretinograms (ERG) which provide an objective measure of retinal function.
A study was conducted where baseline ERG was recorded in rats (n=12 per diet group) before they drank either water, 4.25 mg ACN/kg body weight (BW) or 8.5 mg ACN/kg BW for 3 weeks. ACN was provided as BBJ. After 3 weeks a second set of ERG recordings were taken just before LIR was induced by exposure to moderate light (3000 lux) for 24 hours. After a 3 week recovery period from LIR, a last series of ERGs was taken. Preliminary analysis showed that exposure to this moderate light reduced the ERG activity of non-ACN fed rats by an average of 9.7%. Rats receiving 4.25 mg ACN/kg BW showed a similar LIR-induced ERG deterioration (11.8% reduction, p=0.99 after Bonferonni correction), while rats fed 8.5 mg ACN/kg BW showed no retinal deterioration. In a subsequent study rats (n=12) were submitted to a greater degree of LIR by exposure to brighter light (6000 lux) for 24 h.
After a 3 week recovery period retinal activity in rats that did not receive ACN decreased to 16% of the initial value, while rats fed 8.5 mg ACN/kg BW maintained ERG activity that was 35% of the baseline value, which was twice the amplitude of the control group. Thus both studies demonstrated that BBJ protected retinal activity after LIR. Studies are continuing to examine the effects of ACN on ERG as well as on retinal histology and the concentration of rhodopsin after LIR.
Canter, P. H. and E. Ernst (2004) Anthocyanosides of Vaccinium myrtillus (Bilberry) for Night Vision – A Systematic Review of Placebo-Controlled Trials. Survey Ophthal. 2004 49, 38-50.
Kalt, W.; Dufour, D. Health Functionality of Blueberries
HortTech. 1997, 7, 216 – 221.