Health Benefits of Grapes and Raisins

Grape-enriched diet supports eye health

New research presented May 2014 at the Association for Research in Vision and Ophthalmology conference in Orlando, Florida suggests that regular grape consumption may play a role in eye health by protecting the retina from deterioration. Specifically, a grape-enriched diet resulted in a protective effect on retinal structure and function.

The retina is the part of the eye that contains the cells that respond to light, known as photoreceptors. There are two types of photoreceptors: rods and cones. Retinal degenerative diseases affect over 5 million people in the U.S., and can cause blindness due to photoreceptor cell death.

The study was conducted by a research team at the University of Miami, Bascom Palmer Eye Institute and investigated whether a diet supplemented with grapes could protect the photoreceptors in mice with retinal degeneration. Mice were either fed a grape-supplemented diet corresponding to 3 servings of grapes per day for humans or one of two control diets.

The results showed that retinal function was significantly protected in the mice consuming the grape-enriched diet. The grape-consuming group had three-fold higher rod and cone photoreceptor responses compared with those on the control diets. They also exhibited thicker retinas. Grape consumption also protected retinal function in an oxidative stress model of macular degeneration. Further analysis revealed that the grape diet resulted in lower levels of inflammatory proteins and higher amounts of protective proteins in the retinas.

"The grape-enriched diet provided substantial protection of retinal function which is very exciting," said Dr. Abigail Hackam, lead investigator of the study. "And it appears that grapes may work in multiple ways to promote eye health from signaling changes at the cellular level to directly countering oxidative stress."

Grape consumption may offer benefits for symptomatic knee osteoarthritis

Adding grapes to diet resulted in less pain related to activity

New research presented last week at the Experimental Biology conference in San Diego, California, suggests that regular grape consumption may help alleviate pain associated with symptomatic osteoarthritis of the knee, and improve joint flexibility and overall mobility. Researchers attribute these potential benefits to the polyphenols found in grapes.

The sixteen week clinical study, undertaken by Texas Woman's University, was designed to investigate the benefits of grape consumption on inflammation and osteoarthritis outcomes. 72 men and women with knee osteoarthritis (OA) were assigned to either consume grapes in the form of a whole grape freeze-dried powder, or a placebo powder.

The study results, presented by lead investigator Shanil Juma, Ph.D., showed that both men and women consuming a grape-enriched diet had a significant decrease in self-reported pain related to activity and an overall decrease in total knee symptoms. This beneficial effect was more pronounced in females. Additionally, age-related differences were observed: there was a 70% increase in very hard activity for those under 64 years of age consuming the grape powder, while those receiving the placebo reported a significant decrease in very hard activity. Participants over 65 years, whether consuming grapes or the placebo, reported a decline in moderate to hard activities.

Evidence of increased cartilage metabolism was observed in men consuming the grape-enriched diet; they had higher levels of an important cartilage growth factor (IGF-1) than those on placebo. This protective effect was not observed in the females. The researchers noted that no difference in range of motion was observed for either the grape group or the placebo group. The serum marker for inflammation (IL1-β) measured was increased in both placebo and grape groups, although much less of an increase was observed in the grape group.

"These findings provide promising data that links grape consumption to two very important outcomes for those living with knee osteoarthritis: reduced pain and improvements in joint flexibility," said Dr. Juma. "More research is needed to better understand the results of the serum biomarkers, as well as the age and gender differences observed."

Dr. Juma also shared results from a recent cell study that looked at the effects of whole grape polyphenols on cartilage cell integrity and markers of cartilage health. Cartilage cells were first treated with various doses of whole grape polyphenols, and then stimulated with an inflammatory agent. Cell proliferation significantly increased – in a dose dependent manner – in the grape polyphenol treated cells in the presence of an inflammatory agent. Additionally a marker for cartilage degradation was significantly lower with the three highest doses of the whole grape polyphenols when compared to control cells and cells treated with the inflammatory agent, suggesting a possible protective effect of grapes on cartilage cells.

Osteoarthritis is a condition where the natural cushioning between joints – the cartilage – wears away. Millions of Americans are affected by osteoarthritis: according to the Arthritis Foundation, more than 27 million people have osteoarthritis and knees are an area most commonly affected. Osteoarthritis is more likely to occur in people over 45 years of age, and women are more likely to have osteoarthritis than men.

Grapes reduce heart failure associated with hypertension

A study appearing in the Journal of Nutritional Biochemistry¹ demonstrates that grapes are able to reduce heart failure associated with chronic high blood pressure (hypertension) by increasing the activity of several genes responsible for antioxidant defense in the heart tissue. Grapes are a known natural source of antioxidants and other polyphenols, which researchers believe to be responsible for the beneficial effects observed with grape consumption. This study, funded by a grant from the National Institutes of Health (NIH), and conducted at the University of Michigan Health System, uncovered a novel way that grapes exert beneficial effects in the heart: influencing gene activities and metabolic pathways that improve the levels of glutathione, the most abundant cellular antioxidant in the heart.

An estimated 1 billion people worldwide have hypertension, which increases the risk of heart failure by 2 to 3-fold. Heart failure resulting from chronic hypertension can result in an enlarged heart muscle that becomes thick and rigid (fibrosis), and unable to fill with blood properly (diastolic dysfunction) or pump blood effectively. Oxidative stress is strongly correlated with heart failure, and deficiency of glutathione is regularly observed in both human and animal models of heart failure. Antioxidant-rich diets, containing lots of fruits and vegetables, consistently correlate with reduced hypertension.

In this study, conducted at the University of Michigan Health System, hypertensive, heart failure-prone rats were fed a grape-enriched diet for 18 weeks. The results reproduced earlier findings that grape consumption reduced the occurrence of heart muscle enlargement and fibrosis, and improved the diastolic function of the heart. Furthermore, the mechanism of action was uncovered: grape intake "turned on" antioxidant defense pathways, increasing the activity of related genes that boost production of glutathione.

"Our earlier studies showed that grapes could protect against the downward spiral of hypertensive heart failure, but just how that was accomplished – the mechanism – was not yet known," said lead investigator E. Mitchell Seymour, Ph.D. "The insights gained from our NIH study, including the ability of grapes to influence several genetic pathways related to antioxidant defense, provide further evidence that grapes work on multiple levels to deliver their beneficial effects."

Seymour noted that the next phase of the NIH study, which will continue into 2014, will allow his team to further define the mechanisms of grape action, and also look at the impact of whole grape intake compared to individual grape phytonutrients on hypertension-associated heart failure.

"Our hypothesis is that whole grapes will be superior to any individual grape component, in each of the areas being investigated," said Dr. Seymour. "The whole fruit contains hundreds of individual components, which we suspect likely work together to provide a synergistic beneficial effect."

The insights gained from this research will further the knowledge on grapes and heart health, but will also provide translational information on the value of dietary (whole foods) and dietary supplement approaches for prevention of heart disease stemming from chronic hypertension.

"The NIH grant is allowing the team at the University of Michigan Medical System to expand its work in this important area and further highlight the multi-faceted role of grapes in supporting heart health," said Kathleen Nave, president of the California Table Grape Commission. "This work will also provide key insights into the role of whole fruit versus individual components of a fruit, using grapes as the benchmark."

Raisins provide same workout boost as sports chews

New research (July, 2012) published in the Journal of the International Society of Sports Nutrition suggests that eating raisins may provide the same workout boost as sports chews.

Conducted by researchers at the University of California-Davis, the study evaluated the effects that natural versus commercial carbohydrate supplements have on endurance running performance. Runners depleted their glycogen stores in an 80-minute 75% V02 max run followed by a 5k time trial. Runners completed three randomized trials (raisins, chews and water only) separated by seven days. Findings included:

* Those that ingested raisins or sports chews ran their 5k on average one minute faster than those that ingested only water

* Eating raisins and sports chews promoted higher carbohydrate oxidation compared to water only

"Raisins are a great alternative to sport chews as they also provide fiber and micronutrients, such as potassium and iron, and they do not have any added sugar, artificial flavor or colors," said James Painter, Ph.D., R.D., and nutrition research advisor for the California Raisin Marketing Board. "As an added bonus, raisins are the most economical dried fruit according to the United Stated Department of Agriculture, so they are cost effective and convenient for use during exercise."

Snacking on raisins a heart-healthy way to lower blood pressure

If you have slightly higher than normal blood pressure – known as prehypertension – consider eating a handful of raisins. New data suggest that, among individuals with mild increases in blood pressure, the routine consumption of raisins (three times a day) may significantly lower blood pressure, especially when compared to eating other common snacks, according to research presented March, 2012 at the American College of Cardiology's 61st Annual Scientific Session. The Scientific Session, the premier cardiovascular medical meeting, brings cardiovascular professionals together to further advances in the field.

Even though raisins are popularly cited to lower blood pressure on various websites and are known to have intrinsic properties that could benefit heart and vascular health, researchers believe this is the first controlled study to scientifically support raisins' blood pressure-lowering effects compared to alternative snacks.

"It is often stated as a known fact that raisins lower blood pressure. But we could not find much objective evidence in the medical literature to support such a claim," said Harold Bays, MD, medical director and president of Louisville Metabolic and Atherosclerosis Research Center (L-MARC) and the study's lead investigator. "However, our study suggests if you have a choice between eating raisins or other snacks like crackers and chocolate chip cookies, you may be better off snacking on raisins at least with respect to blood pressure."

In this investigation, Dr. Bays and his team conducted a randomized controlled clinical trial to compare the blood pressure effect of eating raisins versus other snacks in 46 men and women with prehypertension. Participants were randomly assigned to snack on raisins or prepackaged commercial snacks that did not contain raisins, other fruits or vegetables but had the same number of calories per serving three times a day for 12 weeks. The study controlled for individual differences in nutrition and physical activity.

Data analyses found that compared to other snacks, raisins significantly reduced systolic blood pressure at weeks 4, 8, and 12, ranging from -4.8 to -7.2% or -6.0 to -10.2 mmHg (p values <0 -2.4="" -="" .05="" 0.05="" 5.2="" all="" analysis="" at="" blood="" changes="" demonstrated="" diastolic="" from="" group="" mean="" mmhg="" p="" pressure="" raisins="" ranging="" reduced="" significantly="" span="" study="" that="" to="" values="" visits="" with="" within="">

Pre-packaged snacks (including crackers and cookies) did not significantly reduce systolic or diastolic blood pressure at any study visit.

"Overall, these findings support what many people intrinsically believe: that natural foods often have greater health benefits than processed foods," Dr. Bays said.

The study did not identify how raisins lower blood pressure. However, raisins are high in potassium, and have fiber, polyphenols, phenolic acid, tannins and antioxidants.

"Raisins are packed with potassium, which is known to lower blood pressure," Dr. Bays said. "They are also a good source of antioxidant dietary fiber that may favorably alter the biochemistry of blood vessels, causing them to be less stiff, which in turn, may reduce blood pressure."

Although this study was not designed or powered to evaluate for outcomes benefits, other studies support that in patients with prehypertension, mild lowering of blood pressure with medications may have clinical benefits in reducing cardiovascular events.

According to the Centers for Disease Control and Prevention, nearly one in three (28 percent) American adults have prehypertension – defined as a systolic pressure from 120 to 139 millimeters of mercury (mm Hg) or a diastolic pressure from 80 to 89 mm Hg. This study's findings help validate some current nutritional recommendations. For example, 60 raisins – about a handful – contain 1 gram of fiber and 212 milligrams of potassium, which are both recommended in the Dietary Approaches to Stop Hypertension (DASH) diet.