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Hydroxytyrosol is thought to be the main antioxidant compound in olive fruit, and it is believed to play a significant role in many of the health benefits attributed to olive oil. Previous research has linked the compound to cardiovascular benefits, typically reductions in LDL or “bad” cholesterol. Data has also suggested the compound may boost eye health and reduce the risk of macular degeneration.

Spanish researchers reported these results in the British Journal of Nutrition. Twenty-two healthy volunteers between 20 and 45 years of age and with a BMI between 18 and 33 kg/m2 were recruited. Volunteers were randomly assigned to receive 10 to 15 grams per day of hydroxytyrosol-enriched sunflower oil or non-enriched sunflower oil for three weeks. The former provided a daily hydroxytyrosol dose of between 45 and 50 mg. After the initial three week period, volunteers had two weeks of no intervention before crossing over to receive the other intervention.

Results showed no changes in total, LDL, or HDL-cholesterol between the groups. However, consumption of the hydroxytyrosol-enriched sunflower oil produced significant reductions in oxidized LDL from 79.8 units per liter at the start of the study to 64.1 U/l after three weeks, compared to an increase from 72.7 to 86.4 U/l during the control phase. Furthermore, the activity of arylesterase increased from 235.2 to 448.9 U/l during the hydroxytyrosol phase, compared with an increase from 204.1 to 310.3 U/l during the control phase.

The researchers reported that although hydroxytyrosol-enriched sunflower oil did not significantly reduce LDL-cholesterol or increase HDL-cholesterol, it acted as a functional food by increasing arylesterase activity and reducing oxidized LDL. Oxidized LDL is believed to be a major player in promoting atherosclerosis (the build-up of fatty plaques in arteries) and general cardiovascular disease. Based on these results, dietary sources of hydroxytyrosol appear to be capable of reducing certain risk factors associated with coronary artery disease.

Vazquez-Velasco M, et al. Effects of hydroxytyrosol-enriched sunflower oil consumption on CVD risk factors. 2010. Br J Nutr.

Although there are a few published reports regarding the effect of green tea on insulin sensitivity and glucose control in humans, the results have been inconsistent.

In a new study published in the American Journal of Clinical Nutrition, researchers aimed to more accurately quantify the effect of green tea on glucose control and insulin sensitivity.

Researchers completed a thorough literature search to find all randomized controlled trials that included information on the effects of green tea and green tea extracts on insulin sensitivity and glucose control in humans.

There were 17 trials, including a total of 1,133 subjects that met the criteria and were included in this meta-analysis. The studies were mostly of a short duration, and 7 of the studies were considered of high quality.

Overall, green tea consumption significantly reduced fasting glucose and hemoglobin A1c (a long-term measure of blood glucose control). These results were more significant in studies including subjects at risk for metabolic syndrome, and in subject with higher catechin (a compound in green tea) intakes. When only the high quality studies were included, green tea significantly reduced fasting insulin concentrations.

The results of this meta-analysis suggest that green tea intake may lower fasting glucose, insulin and HbA1c concentrations, especially in people at risk for metabolic syndrome. Researchers noted that long-term randomly controlled trials of higher quality should be conducted to further confirm these findings.

Kai Liu et al. Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trial.

Periodontal disease is a common chronic inflammatory disease and a major risk factor for tooth loss.  A study published in the American Journal of Clinical Nutrition has demonstrated a link between low blood levels of vitamin D and the incidence of gum disease.

The study group included over 11,000 adults over the age of twenty. Eighty percent of those studied had inadequate vitamin D levels, and the lower their vitamin D serum levels, the greater the risk of tooth loss. Among subject participants age 50 and older, those with the lowest vitamin D levels had 25 to 27 percent more tooth loss than those in the highest vitamin D range.

The researchers suspect that vitamin D may cut down on the inflammatory response that leads to periodontal disease. Given the high prevalence of periodontal disease and vitamin D deficiency, these findings suggest important oral health implications related to vitamin D intake.

Dietrich T, et al. Association between serum concentrations of 25-hydroxyvitamin D3 and periodontal disease in the US population. Am J Clin Nutr 80(1):108-13.

Age-Related Macular Degeneration (AMD) is the most common cause of vision loss in developed countries. This degenerative eye disease causes damage to the macula (central retina) of the eye, impairing central vision. People affected by AMD have difficulty reading, driving and performing activities that require clear central vision. Many factors contribute to the development of AMD, including aging, genetics, diet, and smoking. The macula is a yellow oval-shaped pigmented area located near the center of the retina. Structures within the macula are specialized to provide high-acuity vision. Lutein and zeaxanthin are found in high concentrations here, giving the macula its yellow color. This protective layer, known as macular pigment, filters harmful high-energy blue wavelengths of light preventing damage to the retina, cones, and rods.

Numerous published studies have previously reported a link to intakes of lutein and zeaxanthin and AMD risk; however, the research has been mostly inconsistent. In this newly published prospective study, researchers used two decades of data involving more than 100,000 participants from the Nurses’ Health Study and the Health Professionals Follow-up Study. All participants were aged 50 years or older and were free of diagnosed AMD, diabetes mellitus, cardiovascular disease, and cancer (except non-melanoma skin cancer) at baseline. The researcher’s analyzed carotenoid intake based on dietary food frequency questionnaires at baseline and follow-up, and then calculated predicted plasma carotenoid scores. The results of this study found that participants with the highest average plasma lutein and zeaxanthin levels had a 40% reduced risk of developing advanced AMD compared to those with the lowest average levels. “Lutein and zeaxanthin form macular pigments that may protect against AMD by reducing oxidative stress, absorbing blue light, and stabilizing cell membranes,” the authors explain.

Dark green leafy vegetables are the primary dietary sources of lutein and zeaxanthin, but they are also found in some other colorful fruits and vegetables. Average dietary intake in the U.S. is only about 1-3 mg/day, far below the amount most studies indicate as a minimum needed to decrease risk of AMD. “Because other carotenoids may also have a protective role, a public health strategy of increasing the consumption of a wide variety of fruits and vegetables rich in carotenoids could be most beneficial and is compatible with current dietary guidelines,” the authors concluded.

JAMA Ophthalmol. 2015;133(12):1415-1424.

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