(1 cup, 130 grams, cooked)
Vitamin K – 1180% Daily value (DV)
Vitamin A – 98% DV
Vitamin C – 71% DV
Manganese – 27% DV
Copper – 22% DV
Kale is rich in many nutrients, but the vitamins and minerals listed above are among the most important to vision health. Vitamins A and C's importance to vision has been widely publicized for decades. Vitamin A / beta carotene protects the surface if the eye (the cornea) and is important to night vision. Vitamin C promotes healthy capillaries and supports the health of ocular blood vessels. Scientific research has shown that vitamin C also lowers the risk of cataracts, in concert with vitamin E (also found in Kale), and slows the progression of age-related macular degeneration (AMD) and visual acuity loss.
Vitamin K is believed to inhibit the calcification of blood vessels, while promoting bone mineralization. The mechanism is not fully understood yet, but vitamin K “appears to be important for the prevention of calcification of soft tissues, including cartilage, vasculature, skin, and trabecular meshwork cells in the eye.”3 The trabecular meshwork cells control intraocular pressure and, therefore, can determine whether or not you develop glaucoma. Manganese deficiency has been linked to many health issues, eye problems among them. And copper is necessary for strong, healthy blood vessels and capillaries, just like vitamin C.
According to Health Magazine, “Oxidative damage—from sunlight, smoking, or everyday contaminants in the environment—are thought to stimulate [AMD], which is why antioxidants are part of the preventive solution.”1 Vitamins A and C and the mineral copper are all antioxidants and, since oxidative stress is thought to be a trigger for AMD, it stands to reason that eating kale would be a simple, yet, effective way to help prevent the disease.
Kale is also a great source of the carotenoids lutein and zeaxanthin, although there is currently no RDA (recommend daily allowance) or DV for these nutrients as yet. “Just one cup of [cooked kale] is packed with more than 20 milligrams of lutein and zeaxanthin—two nutrients that do wonders for your eyes. These nutrients have been shown to reduce the risk of age-related macular degeneration and cataracts.”2 Raw kale contains even more: 39.5mg lutein and 22mg zeaxanthin, per 100 gram serving (100 grams = 0.4 cups).
How much Kale do we need?
Apparently we don't need much. The DV for nutrients are already calculated to insure that the basic health needs of the population are met, so, as long as you get at least 100% total of each nutrient, each day, you can be certain that your vision will have some protection. And, as you can see from the list above, kale contains ample amounts of the aforementioned eye nutrients when cooked, but you could get even more by simply eating kale raw. As you may know, cooking decreases the amount of vitamins and minerals in foods; how much they're decreased depends on the cooking method.
To reiterate, there is no set RDA or DV for lutein or zeaxanthin, however, “Dr. Johanna M. Seddon and associates at Harvard University found that 6 mg per day of lutein led to a 43% lower risk for macular degeneration”4 So, even if you only ate half a cup of kale, whether raw or cooked, you would still be consuming enough kale to cut your AMD risk in half! “The recommended dosage [of lutein] is 6 mg to 30 mg daily.”4
According to Health Magazine, AMD is the number one cause of vision loss for Americans age 55 and older and, according to the World Health Organization (WHO), vitamin A deficiency (VAD) is the number one cause of preventable blindness in children worldwide. Kale contains more eye protecting nutrients than even carrots and, some, in higher amounts. Lutein, zeaxanthin, vitamins A and C, the minerals manganese and copper have all been recognized as either necessary for maintaining good eye health and/or capable of preventing vision loss.
There's no doubt that kale is an acquired taste for many, especially raw, but it's nutrient content can prevent vision loss in both children and adults, decreasing one's risk of developing AMD, as well as glaucoma, cataracts and other eye ailments. So, despite the flavor, kale is a food well worth adding to the menu.
A blog by holistic health writer Andrea Lewis
1 Upton, Julie. “For Healthy Eyes, Think Broccoli and Kale, Not Carrots”. Health Magazine, September 22, 2008. <news.health.com> Web. January 2, 2016
2 McMullen, Laura. “13 Foods That Do Your Eyes Good”. U.S. News & World Report Health, March 12, 2013. Web. February 2, 2016
3 Higdon, Jane, PhD. “Vitamin K”. Linus Pauling Institute/Oregon State University, 2000. Web. February 2, 2016
4 Torrey, George, PhD. “Lutein May Decrease Your Risk of Macular Degeneration”. American Macular Degeneration Foundation, n.d. Web. February 3, 2016
“Kale.” The World's Healthiest Foods, n.d. Web. February 2, 2016
I Perlman, B Barzilai, T Haim and A Schramek. “Night vision in a case of vitamin A deficiency due to malabsorption”. British Journal of Ophthalmology, January 1983. Web. February 2, 2016
“Vitamin C”. American Optometric Association, n.d. Web. February 2, 2016