Green Leafy Vegetables are Nutritional Stand-Outs

December 26, 2008

This is a well documented nutrition article based on peer reviewed article. Kale, spinach, and brussel sprouts are among the most delicious of vegetables, plus are power-houses of good nutrition. All the more reason to Go Veg and eschew the cruel flesh-based standard American diet. Margarethttp://findarticles.com/p/articles/mi_m0813/is_6_34/ai_n27333489The greens partyBonnie Liebman Spinach,

kale, collards, mustard greens, beet greens, romaine lettuce, and other

leafy greens. They're the standout vegetables, jam-packed with vitamins

A, C, and K, folate, potassium, magnesium, iron, lutein, and

phytochemicals.

And it's not unusual to see studies on diet and disease give them

special recognition with a phrase like "vegetables--especially green

leafy vegetables--were associated with a lower risk of...."

All vegetables are good vegetables (except, perhaps, white

potatoes). But greens have something more going for them. Here's a

sampling of some findings--and a few hunches--that may explain what's

so good about greens.

EYES

As you age, your eyes age.

The older lens no longer adjusts as well to see accurately at

different distances, and the older pupil no longer dilates as much to

let light reach the retina. An 80-year-old retina receives one-sixth

the light of a 20-year-old retina in a well-lit room and one-sixteenth

as much light in a darker room.

Worse yet, the older eye is more vulnerable to cataracts (clouded

lens) and macular degeneration (deterioration of the center of the

retina, or macula). Macular degeneration is the leading cause of

blindness in people over the age of 60.

On the bright side, two carotenoid pigments in leafy greens--lutein

and zeaxanthin--may help protect both the lens and the retina.

"Leafy greens are incredibly high in lutein and zeaxanthin, so just

one or two servings a week places people in the highest intakes," says

Julie Mares of the Department of Ophthalmology and Visual Sciences at

the University of Wisconsin.

Researchers got interested in the two carotenoids in part because

both concentrate in the eye. "The macular pigment is composed of lutein

and zeaxanthin," says Mares. "The concentration in the macula is

100-fold higher than in the blood."

What's more, she adds, "they're the only carotenoids that

accumulate in the lens, though the level in the lens is much lower than

in the macula."

How might lutein and zeaxanthin protect the eye?

"In both the lens and the retina, we suspect that they act as

antioxidants that scavenge marauding oxygen molecules called free

radicals," says Mares.

"In the retina, we think that they also act as a filter that

absorbs short wavelength--or blue--light, which is toxic to the retina."

But the human evidence that leafy greens--or lutein and zeaxanthin--can protect the eye is still modest.

In several large studies, people who reported consuming the most

lutein and zeaxanthin had a 20 to 50 percent lower risk of cataract

extractions. (1,2) Other studies found a lower risk of macular

degeneration in people who consumed the most lutein and zeaxanthin.

(3,4) However, some studies found no link or only saw it in women

younger than 75. (5,6)

"The data are stronger for cataracts than for macular degeneration

to date," says Mares. But that could be because cataracts are so much

more common, which makes them easier to study.

Bottom line: it's too early to conclude that lutein and zeaxanthin

can protect the eyes, but it's still worth eating leafy greens. "I do,"

says Mares. "They're so rich in micronutrients, there's sufficient

evidence that they may protect the eyes, and there's no evidence that

they're deleterious."

BONES

Which foods keep your skeleton strong? Most people would never

think of kale, collards, spinach, and other greens as bone builders.

Yet researchers suspect that green leafy vegetables protect bone because they're loaded with vitamin K.

"They're the best known source of vitamin K," says Sarah Booth of

the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts

University in Boston. "It's part of photosynthesis, so anything that's

green has vitamin K."

Vitamin K is best known for its ability to help blood clot, but a growing body of evidence suggests that it does much more.

"Vitamin K is important for proper functioning of bone-dependent

proteins," explains the Research Center's Katherine Tucker. "Bone is

constantly breaking down and rebuilding, and it needs those proteins to

rebuild."

When Tufts researchers looked at nearly 900 men and women in the

Framingham Heart Study, those who consumed roughly 250 micrograms of

vitamin K a day (largely from food) had a 65 percent lower risk of hip

fractures than those who averaged around 55 micrograms a day. (7)

And in another study, of nearly 1,500 Framingham women, those who

consumed more than about 200 micrograms of vitamin K a day had greater

spine and hip bone density than those who typically ate less than about

100 micrograms a day. (8)

The question is whether it's vitamin K, something else in leafy

greens, or something else about people who eat leafy greens that

protects their bones. "People who eat leafy greens also eat a healthier

diet and lead a healthier lifestyle," says Booth.

So clinical trials have given women either a placebo or vitamin K

(with or without vitamin D) to see if it boosts their bone density.

Three trials--testing 200 to 1,000 micrograms of vitamin K per

day--have been done so far. (9-11)

"A Dutch study found less bone loss at the hip, a British study

found less bone loss only at the wrist, and a University of Wisconsin

study found no effect anywhere," says Booth. "So the results are

inconsistent."

Two larger studies--one at Tufts and one at the University of

Toronto--are due out within the next year. "Together, they'll have 900

men and postmenopausal women, so that should answer the question," says

Booth.

In the meantime, you can easily get enough vitamin K from greens.

"You can get 500 micrograms in just half a cup of cooked collards,"

says Booth.

And even if the vitamin K in greens doesn't make bones denser, the greens may still strengthen your skeleton.

In several studies, people who reported eating more of any fruits

and vegetables had higher bone density. (12,13) Researchers think

that's because the potassium, magnesium, and other alkaline-forming

minerals in produce neutralize acid-forming foods in the body.

"We get acids from the metabolism of foods like meat, some grains,

and food additives like phosphoric acid in colas," says Tufts' Tucker.

(What matters isn't whether a food contains acid, but whether it

makes the blood more acidic once the food is broken down and absorbed,

she adds. Orange juice, for example, contains citric acid but makes the

blood more alkaline.)

"If there's enough potassium, magnesium, and calcium in the diet,

those minerals neutralize the acidic compounds," Tucker explains. "But

if there's not enough alkaline to do the job, the blood gets acidic."

The body has to keep the acid-base balance in the blood within an

extremely narrow range, she adds, "so it takes calcium out of bone to

keep the balance."

Taking calcium from bones is no problem if it happens occasionally.

"But if it happens continually, it's a major contributor to lower bone

mineral density," says Tucker.

THE BRAIN & BEYOND

Researchers are hunting down clues that leafy greens may do more. For example:

* Memory. Women who consumed the most leafy greens had less

cognitive decline--that is, a smaller drop in memory and other test

scores over two years--than did women who consumed the fewest green

leafy vegetables. (14)

* Diabetes. When researchers studied nearly 40,000 female health

professionals, they found no link overall with fruits and vegetables.

But among overweight women, those who consumed the most green leafy

vegetables had about a 15 percent lower risk of diabetes than those who

consumed the least. (15)

* Colon Cancer. Men who consumed the most green leafy vegetables

(about two servings per day) had a 14 percent lower risk of colorectal

cancer than those who consumed the least (about one serving per week).

(16)

Some researchers think that the chlorophyll in green vegetables may

counter the harm caused by heme, the iron-carrying pro-oxidant pigment

that gives meat its red color. Feeding heme to rats makes their colon

cells proliferate more, but adding either spinach or purified

chlorophyll to their diet reverses the damage. (17)

* Stroke. In a study of more than 75,000 women and 38,000 men, the

risk of non-hemorrhagic stroke (which accounts for 80 percent of all

strokes in the United States) was about 20 percent lower for every

serving of green leafy vegetables people consumed per day, though other

vegetables were also linked to a lower risk. (18)

And if those potential benefits--which need to be confirmed--aren't

convincing, it's indisputable that leafy greens are a low-calorie,

nutritional powerhouse.

"They've got vitamin K, potassium, and magnesium, along with

antioxidants and other phytochemicals that are not well understood but

that may also have protective effects," says Tucker. "They're super

foods."

(1) Am. J. Epidemiol. 149: 810, 1999.

(2) Am. J. Clin. Nutr. 70: 509, 517, 1999.

(3) Am. J. Epidemiol. 153: 424, 2001.

(4) Invest. Ophthalmol. Vis. Sci. 47: 2329, 2006.

(5) Arch. Ophthalmol. 124: 1151, 2006.

(6) Ophthalmology 109: 2272, 2002.

(7) Am. J. Clin. Nutr. 71: 1201, 2000.

(8) Am. J. Clin. Nutr. 77: 512, 2003.

(9) Osteoporos. Int. (Feb. 8, 2007), doi:10.1007/s00198-007-0337-9.

(10) J. Bone Miner. Res. 22: 509, 2007.

(11) www.uwosteoporosis.org/Pdf%20land/ VitKabstract.pdf.

(12) Am. J. Clin. Nutr. 69: 727, 1999,

(13) Am. J. Clin. Nutr. 79: 155, 2004.

(14) Ann. Neurol. 57: 713, 2005.

(15) Diabetes Care 27: 2993, 2004.

(16) Am. J. Epidemiol. doi:10.1093/aje/kwm067.

(17) Carcinogenesis 26: 387, 2005.

(18) JAMA 282: 1233, 1999.

Greens with EnvyMost green leafy vegetables supply not just vitaminK and lutein, but one to three days' worth ofvitamin A and 10% to 20% of a day's vitamin C andfolate. (If you take Coumadin or other blood thinners,ask your doctor to adjust the dose to accommodatethe vitamin K in the greens you eat regularly.)Vegetable(1/2 cup cooked, Vitamin K Lutein *unless noted) (mcg) (mcg)Kale 530 11,900Spinach 440 10,200Swiss chard 290 9,600Collards 500 7,300Turnip greens 260 6,100Mustard greens 210 4,200Spinach (1 cup raw) 140 3,700Dandelion greens 100

2,500Beet greens 350 1,300Romaine lettuce (1 cup raw) 50 1,100Boston (Bibb) lettuce (1 cup raw) 60 700Parsley (10 sprigs raw) 160 600Iceberg lettuce (1 cup raw) 20 200* Includes zeaxanthin.Source: U.S. Dept. of Agriculture.