Friday, February 29, 2008

Low vitamin D levels may increase heart disease risk

A new study published in the journal Circulation showed that low levels of vitamin D may increase the risk of cardiovascular events, including heart attack, heart failure, or stroke. And, those with both hypertension and low vitamin D levels had nearly double the risk of cardiovascular problems.

Interest in vitamin D has been increasing in recent months with a growing number of studies linking the vitamin to protection against osteoporosis and certain cancers. There is also evidence that a higher intake of vitamin D may be helpful with regard to high blood pressure, fibromyalgia, diabetes mellitus, multiple sclerosis, and rheumatoid arthritis.

In a new study, researchers used data from the 1739 participants in the Framingham Offspring Study to study the relationship between vitamin D levels and cardiovascular health risk. Although vitamin D levels above 30 ng/mL are considered optimal for bone metabolism, only 10 percent of the participants had levels in this range. In fact, 28 percent had blood levels lower that 15 ng/mL. Participants with levels below 15 ng/mL had a 62 percent greater chance to develop cardiovascular events than those with higher levels. People with low vitamin D levels and high blood pressure (> 140 and 90 mmHg), were found to have double the risk of cardiovascular problems compared to people with normal blood pressure and vitamin D levels.

Vitamin D is produced in the skin on exposure to UVB radiation (sunlight) and obtained in the diet from foods like oily fish, egg yolk, and liver. Recent studies have shown, however, that sunshine levels in some northern countries are so weak during the winter months that the body makes little to no vitamin D at all, leading to widespread deficiencies of the vitamin. In addition, increased skin pigmentation also reduces the effect of UVB radiation, meaning darker skinned people are more at risk.

The results from this study raise the possibility that treating vitamin D deficiency, by supplementation and/or lifestyle measures, could reduce the risk of cardiovascular events.

Source: Vitamin D Deficiency and Risk of Cardiovascular Disease, Wang et al, Circulation 2008 Jan 29;117(4):503-11.

Thursday, February 21, 2008

Higher plasma vitamin C concentrations predict lower risk of stroke in adults

In a British study of over 20,000 adults, those with the highest plasma vitamin C levels had a significantly lower risk of stroke when compared to adults with lower levels.

To date, clinical trials have not shown significant benefit of vitamin C supplementation in reducing stroke risk, but they have not examined the relation between plasma vitamin C concentrations and stroke risk in a general population.

A recent study published in the American Journal of Clinical Nutrition examined the relation between baseline plasma vitamin C concentrations and risk of incident stroke in a British population of over 20,000 adult men and women. The participants completed a health questionnaire and attended a clinic during 1993 to 1997.

After an average follow-up time of 9.5 years, the participants in the top fourth of plasma vitamin C levels had a 42% lower risk of stroke compared to those with the lowest levels. These results were independent of age, sex, smoking, BMI, blood pressure, cholesterol, physical activity, diabetes, social class, alcohol consumption, and any supplement use.

Plasma vitamin C concentrations, therefore, may act as an indicator of lifestyle or other factors associated with reduced stroke risk and may be helpful in determining those at high risk of stroke.

Source: Plasma vitamin C concentrations predict risk of incident stroke over 10 y in 20 649 participants of the European Prospective Investigation into Cancer – Norfolk prospective population study, Myint et al, American Journal of Clinical Nutrition, Vol. 87, No. 1, 64-69, January 2008

Thursday, February 14, 2008

Regular exercise and fish oil may keep arteries clear and reduce body fat

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A combination of prolonged exercise and fish oil can dramatically reduce levels of a fat that can cause hardening of the arteries, a leading cause of heart disease. Fat in the bloodstream is a primary contributor to atherosclerosis, or partial blockage of the arteries.

A recent study found that people who do prolonged aerobic exercise have muscle cells that are able to quickly break down and reduce levels of a fat called triglycerides. Taking a fish oil supplement can reduce triglyceride levels even more.

The researchers studied triglyceride levels in recreationally active men after they'd eaten high-fat meals. One group ate a fatty meal after they exercised. A second group ate a high-fat meal after taking a four-gram fish oil supplement. A third group ate a high-fat meal after exercising and taking the fish oil supplement. A control group ate a high-fat meal only.

The study found a 38 percent decline in peak triglyceride levels in the men who took a fish oil supplement before they ate a high-fat meal. Peak triglyceride levels dropped 50 percent in the men who exercised and took a fish oil supplement before they ate a high-fat meal.

Regular exercise and fish oil supplements may be beneficial for people who are concerned about maintaining a healthy triglyceride level.

Source: Exercise plus n-3 fatty acids: additive effect on postprandial lipemia, Smith BK et al, Metabolism, 2004 Oct;53(10):1365-71.

In a similar, more recent study, combining fish-oil supplements with regular exercise improved both body composition and heart disease risk factors. Overweight participants with various heart disease risk factors were assigned to one of three groups: fish oil (approximately 1.9 grams/day of omega-3 fats), fish oil and exercise, or placebo (sunflower oil).

The exercise group walked 3 days/week for 45 minutes. Heart disease risk factors and body composition were measured at 0, 6, and 12 weeks. The group taking fish oil had a significant reduction in triglycerides, increased HDL cholesterol, and improved arterial vasodilation (blood flow). Both fish oil and exercise independently reduced body fat.

This study showed that increasing intake of omega-3 fatty acids could be a useful addition to exercise programs aimed at improving body composition and decreasing cardiovascular disease risk.

Source: Combining fish-oil supplements with regular aerobic exercise improves body composition and cardiovascular disease risk factors, Alison M Hill, Jonathan D Buckley, Karen J Murphy and Peter RC Howe, Am J Clin Nutr. 2007 May;85(5):1267-74.

Thursday, February 07, 2008

Polyphenols reduce absorption of toxic by-products of a fatty meal

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Polyphenols are antioxidants found in many plants and foods, including grapes, green tea, chocolate, and red wine. They are known to play a role in the prevention of cardiovascular disease, but their specific actions are not entirely understood. New research illustrates the beneficial protective effects of dietary polyphenols taken with a meal.

Researchers recently investigated the impact of red wine polyphenols on the levels of malondialdehyde (MDA), a natural by-product of fat digestion known to increase risk for heart disease and other chronic conditions. In a randomized crossover study, participants were fed three different meals consisting of dark meat turkey cutlets.

The control meal consisted of turkey meat and water. The second meal consisted of turkey meat with polyphenols added after cooking (concentrated wine) followed with a glass of red wine (about 7 ounces). The third meal consisted of turkey meat with polyphenols added before cooking and then followed by a glass of wine.

At various stages of the study, researchers measured blood and urine levels of MDA and found that levels nearly quintupled after the control meal, while increases in MDA levels were completely prevented after subjects consumed the meals with polyphenols.

This study suggests that red wine polyphenols exert a beneficial effect by inhibiting absorption of MDA, a compound toxic to cells. In addition, these results demonstrate the potentially harmful effects of oxidized fats found in foods and the important benefit of dietary polyphenols in a meal.

Source: A novel function of red wine polyphenols in humans: prevention of absorption of cytotoxic lipid peroxidation products, Gorelik, Ligumsky, Kohen and Kanner, FASEB J. 2008 Jan;22(1):41-6.

Wednesday, February 06, 2008

Low-glycemic meals produce favorable leptin and insulin responses, resulting in lower food consumption

Low-glycemic meals promote a post-meal environment that is favorable for reduced food consumption. This may be an advantage in the control of obesity and related disorders, including insulin resistance and type-2 diabetes.

In a recent study, metabolic effects of meals with varying glycemic index (GI) were evaluated. In a group of healthy volunteers, glucose, insulin, and leptin responses to two contrasting breakfast cereals were measured. Leptin is a hormone produced by fat cells that indicates the degree of hunger to the hypothalamus of the brain. Lower leptin levels trigger a sense of satiety and decreased hunger.

Meals were provided on two separate occasions in random order after a 12-hour overnight fast, and consisted of 50 g of available carbohydrate from either Corn Flakes (Kellogg's), or Fiber One (General Mills). Blood samples were obtained at rest, and 30, 60, 90 and 120 min after eating. The GI was calculated from the glucose response to the test meal normalized against a 50 g oral glucose load. The average GI for Corn Flakes was 125 and 49 for Fiber One. These meals were classified as high GI and low GI, respectively, and were significantly different from each other.

The insulin response following the low glycemic meal was significantly reduced compared to the high glycemic meal. The high glycemic meal significantly suppressed circulating leptin levels compared to the low glycemic meal. Lower insulin response and higher circulating leptin levels suggest that low-glycemic meals promote a post-meal environment that is favorable for reduced food consumption; this may be advantageous in the control of obesity and related disorders including insulin resistance and type 2 diabetes.

Source: A High Glycemic Meal Suppresses the Postprandial Leptin Response in Normal Healthy Adults, Barkoukis et al, Ann Nutr Metab 2007 Dec 10;51(6):512-518