Black Currants and Eye Health

Black Currants and Eye Health

Black currants or black currant berries (Ribes nigrum) are small (less than ½ inch), dark purple, mildly sweet seed-containing berries. Black currants are berries generally grown on perennial shrubs, mainly cultivated in Northern Asia, Europe and New Zealand. Scientific evidence has shown that black currants are packed with antioxidant, antibacterial, and antiviral properties. Black currants and the leaves from the shrub have been used in traditional medicine in Asia and Europe to treat a variety of ailments. Black currants are often used in jams, jellies, juices. The fruit is also the main ingredient in the French specialty cassis liqueur.  

 

Black Currant is a source of Vitamin C and also many minerals.

Vitamin C (L-ascorbic acid) is a well known antioxidant and scavenger of damaging free radicals. Studies have shown that black currants contain up to 280mg Vitamin C per 100grams of fresh fruit, making them an important source. Keep in mind that a medium orange has only 50mg per 100grams, and broccoli has 90mg per 100grams. In Britain, during the Second World War, the government recommended that people increase their consumption of black currants. Black currant syrup was freely distributed, especially for children, for the high levels of Vitamin C, to make up for the lack of other fruit available. 

Black currants also are a source of important minerals and have high levels of potassium, calcium, magnesium and iron.

Black currants also contain γ-linolenic acid, an essential polyunsaturated fatty acid. Essential means that it is a fatty acid needed for good health, but our bodies cannot make it, so we must get from dietary sources.

How can black currants help eye health?

Antioxidants & Anthocyanins

Flavonoids are plant-based, biologically active, water-soluble compounds that are powerful antioxidants. They include the pigments that give fruit and vegetables their vibrant colors, such as anthocyanins and flavones. Interestingly, flavonoids are also scavenged by butterflies to give their wings rich color. The main health benefits of black currants come from their deep color and rich source of anthocyanins, which are compounds that have important antioxidant and anti-inflammatory action. Black currants have anthocyanin concentrations up to four-times greater than other commonly known berries and fruits. Levels have been observed as high as 300mg per 100 grams of fruit.

Anthocyanins are derived from anthocyan, the pigment that determines the red, blue and violet colors of flowers and fruits. In plants, anthocyanins have been shown to protect cells from photo-damage by absorbing blue-green light, thereby protecting the cells from high light stress. We can benefit similarly when we eat fruit containing these compounds, the anthocyanins can protect our cells from light damage. Black currants have been shown to possess up to 15 anthocyanins.  

These anthocyanins, the compounds responsible for the deep color of black currants has been shown to be highly bioavailable to eye tissues, meaning that the nutrients from the fruit are accessible for our eyes to use for important biological processes and chemical reactions. 

Research has shown that anthocyanin-rich black currants may have to ability to inhibit multiple biological pathways in the retina to protect visual function. [4] The increased levels of antioxidant defense, suppress the chemical reactions that cause inflammation in its early stages, and reduce the occurrence of retinal cell death, having a tissue-protecting effect. [8]  

 

Macular Degeneration

Macular degeneration causes devastating vision loss for millions of older people. There has been a great deal of research into ways that people can reduce their risk of getting age-related macular degeneration as they get older. There is clinical evidence that shows that daily intake of anthocyanins can significantly reduce the risk of advanced macular degeneration. Their ability to improve blood flow to eye tissues, anti-inflammatory activity, and antioxidant benefits all lead to neuroprotective effects for our retina, and more specifically our macula. [6, 7]

 

Dark Adaptation and Eye Fatigue

One of the benefits of anthocyanins is that it helps form the building blocks of rhodopsin, which is key to our ability to adapt to dim and dark light conditions. People who ate 50mg of black currants (about 1 tablespoon) were able to fully adapt from bright sunlight to darkness much sooner than people who did not receive black currants. Also, anthocyanins can cause relaxation of blood vessels, which has been associated with improvements in eye function and reducing eye fatigue in a study where people looked at a computer screen for extended periods. [5]

 

Glaucoma

The benefits of black currants have also been studied in people who have glaucoma, an eye disorder that can involve elevated pressure inside the eye, leading to vision loss from damage to the optic nerve. Study results have shown that people who consumed 50mg black currants daily were found to have improved blood flow in their eyes, a decrease in elevated intraocular pressure (pressure inside the eye), and reduced visual field loss compared to those that did not receive any black currants. [1, 2, 3]

 

What nutrients are packed into blackcurrants? 

According to the United States Department of Agriculture 1 cup of raw black currants has:

• 70.5 calories
• 17.2 grams carbohydrates
• 1.6 grams protein
• 0.5 gram fat
• 203 milligrams vitamin C (338% DV)
• 0.3 milligram manganese (14 % DV)
• 1.7 milligrams iron (10 % DV)
• 361 milligrams potassium (10 % DV)
• 26.9 milligrams magnesium (7 % DV)
• 66.1 milligrams phosphorus (7 % DV)
• 1.1 milligrams vitamin E (6 % DV)
• 61.6 milligrams calcium (6 % DV)
• 258 IU vitamin A (5 % DV)
• 0.1 milligram copper (5 % DV)
• 0.1 milligram thiamine (4 % DV)
• 0.1 milligram vitamin B6 (4 % DV)
• 0.4 milligram pantothenic acid (4 % DV)

 

References:

[1] 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

[2] 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

[3] 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 https://hirosaki.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3602&item_no=1&attribute_id=20&file_no=1

[4] Miyake S, Takahashi N, Sasaki M, Kobayashi S, Tsubota K, Ozawa Y. Vision preservation during retinal inflammation by anthocyanin-rich bilberry extract: cellular and molecular mechanism. Lab Invest. 2012;92:102–9. https://www.ncbi.nlm.nih.gov/pubmed/21894150

[5] Nakaishi, H. Matsumoto, S. Tominaga and M. Hirayama, Effects of blackcurrant anthocyaoside intake of dark adaptation and VDT work induced transient refractive alteration in healthy humans, J. Altern. Complementary Med., 2000, 6, 553–562. https://www.ncbi.nlm.nih.gov/pubmed/11134978

[6] Pemp, Berthold, and Leopold Schmetterer. “Ocular blood flow in diabetes and age-related macular degeneration.” Canadian Journal of Ophthalmology/Journal Canadien d’Ophtalmologie 43.3 (2008): 295-301. 

[7] Payne AJ, Kaja S, Naumchuk Y, Kunjukunju N, Koulen P. Antioxidant drug therapy approaches for neuroprotection in chronic diseases of the retina. Int J Mol Sci. 2014; 15:1865-86. https://www.ncbi.nlm.nih.gov/pubmed/24473138

[8] Wang Y, Zhao L, Lu F, Yang X, Deng Q, Ji B, Huang F.  Retinoprotective Effects of Bilberry Anthocyanins via Antioxidant, Anti-Inflammatory, and Anti-Apoptotic Mechanisms in a Visible Light-Induced Retinal Degeneration Model in Pigmented Rabbits. Molecules. 2015 Dec 14;20(12):22395-410. https://www.ncbi.nlm.nih.gov/pubmed/26694327