Evidence for Vitamins and Nutrition in Cardiovascular Disease?

Linda Brookes, MSc

Medscape Cardiology.  2007; ©2007 Medscape
Posted 08/07/2007

In trial after trial, antioxidant vitamin supplementation has failed to show benefit as protection against cardiovascular disease progression or events. Nevertheless, the possibility that dietary and enzymatic supplementation could serve at least adjunctive roles in treating cardiovascular risk and disease remains attractive, and new studies continue to be reported. Several new results presented at the 2007 European Atherosclerosis Society (EAS) conference on the effects of diet and dietary supplements on lipids and atherosclerosis provided both positive and neutral evidence as to whether atherosclerosis can be prevented or improved by nonpharmacologic treatment.

Long-term Treatment With Folic Acid, Vitamin B6, and Vitamin B12

Presenter: Kathleen Potter, MBChB, PhD (University of Western Australia, Perth, Australia)

Evidence that long-term treatment with folic acid, vitamin B6, and vitamin B12 does not improve vascular structure or function was presented by Dr. Potter.[1] The new findings come from a cross-sectional study in patients enrolled in VITAmins TO Prevent Stroke (VITATOPS) study.

The VITATOPS trial (http://vitatops.highway1.com.au/index.htm) is an ongoing international, multicenter, randomized, double-blind, placebo-controlled clinical trial investigating whether lowering homocysteine with a combination of folic acid, vitamin B6, and vitamin B12 can reduce the risk for secondary stroke and other serious vascular events in patients with recent stroke or transient ischemic attack of the brain or eye.[2] The trial is coordinated from Royal Perth Hospital and is planned to run until the end of 2008/early 2009. It is supported by the Health Department of Western Australia, National Health and Medical Research Council of Australia (NHMRC), the National Heart Foundation of Australia, and Blackmores (Balgowlah, New South Wales) -- the company that supplies the vitamins.

Evidence from previous studies has suggested that homocysteine is a risk factor for progression of atherosclerosis, and although it has not been conclusively demonstrated to cause atherosclerosis, evidence from human and animal studies has suggested that it can cause changes in vascular structure and function that are typical of atherosclerotic disease. Further, plasma homocysteine concentration has been shown to be an independent predictor of increased carotid intima-media thickness (CIMT), an early physiologic structural change that occurs in the artery wall during the development of atherosclerosis, and homocysteine is also known to impair endothelial function. Elevated plasma homocysteine levels thus increase the risk for an atherothrombotic event, and it has been suggested that this risk could be managed by administration of folic acid (folate), vitamin B6 (pyridoxine), and vitamin B12 (cobalamin).

VITATOPS

In the VITATOPS trial, patients are randomized within 7 months of a stroke or transient ischemic attack to treatment with folic acid 2 mg, vitamin B6 25 mg, and vitamin B12 0.5 mg, administered as a single daily combination tablet, or placebo. To date, approximately 7000 patients, out of a planned total of 8000, have been enrolled in the trial worldwide. The cross-sectional substudy reported at EAS, to test the effects of B vitamins on vascular structure and function, was carried out in patients enrolled in VITATOPS in Perth between 1998 and 2003.

For the substudy a total of 173 subjects (87 randomized to vitamins and 86 randomized to placebo) were recruited and 162 (79 and 83, respectively) were available for analysis. Both groups (mean age, 65 years; approximately 60% men) were well matched at baseline except that the placebo group had higher mean levels of homocysteine (12.2 vs 10.8 micromoles (mcmol)/L, respectively; P =02) and serum vitamin B6 (45 vs 38 nmol/L; P =06); the investigators believe that this was a play of chance at randomization, possibly due to higher folate levels in the subjects randomized to vitamins. The 2 groups were well matched in other characteristics, such as blood pressure, cholesterol, body mass index (BMI), and antiplatelet and anticoagulant medication, at baseline and at follow-up -- almost 4 years later.

The vascular structure measurements were taken when subjects attended a leadoff study session following an overnight fast, having been asked to abstain from caffeine, alcohol, and tobacco for 6 hours prior to the study session and not to take their morning medications, including the VITATOPS tablet. All measurements were made by 1 blinded observer. Vascular structure was assessed by CIMT, with B-mode ultrasound measured to the far wall of the carotid artery and with IMT defined as the distance between the lumen-intima and media-adventitia interfaces. Vascular function was defined as flow-mediated dilation (FMD) in the brachial artery, also measured on B-mode ultrasound, as the change in artery diameter after an ischemic stimulus.

After a mean treatment period of 3.9 years, the vitamin-treated subjects had significantly lower plasma homocysteine levels than the placebo-treated subjects, 7.9 vs 11.8 mmol/L (P <001) and also vs baseline (P <001). This represented a total reduction in homocysteine of approximately 27%. Despite these reductions in homocysteine, however, there was no significant difference between the placebo and vitamin groups in CIMT or in percentage change in FMD from baseline diameter ( Table 1 ), suggesting that there was no obvious improvement in vascular structure or function after long-term homocysteine lowering.

Dr. Potter noted that these results support those of some previous reports, adding that out of some 27 published studies investigating the effect of folate on FMD, about two thirds showed benefit. Dr. Potter has carried out a meta-analysis of these studies (in press), in which, she said, there appeared to be conflict between the short- and long-term studies. Studies that showed benefit tended to use high-dose folate and for relatively short treatment periods of 6-8 weeks, whereas other long-term studies, of about 1-2 years of treatment, showed no benefit on FMD.

Effect of Traditional Mediterranean Diet on Oxidized Low-Density Lipoprotein

Presenter: María-Isabel Covas, MSc, PhD (Municipal Institute for Medical Research [IMIM], Barcelona, Spain)

New findings from the PREvención con DIeta MEDiterránea (PREDIMED) study suggest that one of the ways in which the traditional Mediterranean diet exerts a protective effect against coronary heart disease (CHD) is by reducing the oxidative damage to low-density lipoprotein (LDL).[3] This is further evidence to recommend the traditional Mediterranean diet as a useful tool against atherosclerosis development, particularly in individuals at high risk of developing CHD, said presenter Dr. Covas.

Adherence to the traditional Mediterranean diet has been shown to be associated with a reduction in CHD, cancer, and overall mortality. The protective effect has been attributed, at least in part, to the diet's richness in antioxidants. Adherence to a Mediterranean-type diet has been shown to be associated with lower in vivo plasma-oxidized LDL in a cross-sectional study and in a linear intervention study in healthy women.[4,5] However, despite the widely appreciated richness of the Mediterranean diet in antioxidants, no randomized controlled trials have assessed its effect on in vivo lipoprotein oxidation. Current evidence has indicated that oxidative damage is a promoter of pathophysiologic changes occurring in oxidative stress-associated diseases, such as CHD, cancer, and neurodegenerative and aging, and it is generally thought that oxidized LDL lipoproteins may play a major role in atherosclerosis and cardiovascular disease.

Study Design

The PREDIMED study (www.predimed.org) is an ongoing large, parallel-group, multicenter, randomized, controlled clinical trial that is investigating the effects of the traditional Mediterranean diet on the primary prevention of cardiovascular disease. Once fully enrolled, an estimated 9000 high-risk participants will have been assigned to one of the 3 diet interventions.

The primary outcome is an aggregate of cardiovascular events (cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke). The anticipated follow-up duration is 5 years, and the trial is expected to be completed by December 2010.

At the 2007 EAS meeting, Dr. Covas presented the results of an investigation into the 3-month effects of the dietary interventions on oxidized LDL in 772 participants who were enrolled in PREDIMED between October 2003 and March 2004 in primary care centers affiliated with 10 teaching hospitals across Spain. These participants were community-dwelling men aged 55-80 years and women aged 60-80 years who fulfilled at least 1 of 2 criteria -- either type 2 diabetes or 3 or more of the following CHD risk factors:

  • Current smoking;

  • Hypertension (blood pressure > 140/90 mm Hg or treatment with antihypertensive drugs);

  • LDL cholesterol ≥ 4.14 mmol/L (≥ 160 mg/dL) or treatment with hypolipidemic drugs; and

  • HDL cholesterol ≤ 1.04 mmol/L (≤ 40 mg/dL), BMI ≥ 25 kg/m2, or a family history of premature CHD.

Interim Study Methods and Results

The 772 interim study participants were randomized for 3 months to one of the 3 diets:

  • Low-fat diet (n = 257);

  • Traditional Mediterranean diet plus virgin olive oil (n = 257); or

  • Traditional Mediterranean diet plus virgin olive oil plus mixed nuts (n = 258).

The participants on either of the 2 Mediterranean diets received nutritional education consisting of detailed information about the diet, a 1-hour group session, personalized dietary advice, and advice to increase consumption of vegetables, nuts, and fish. In addition, each group assigned to the Mediterranean diet received, according to randomization, either free virgin olive oil for all the family (1 L/week for cooking and dressing food) or free nuts (sachets of walnuts, hazelnuts, and almonds for an individual dose of 30 g/day).

Participants allocated to the low-fat diet were advised to reduce intake of all types of fat, and were given a leaflet with written recommendations according to the American Heart Association guidelines.[6]

Adherence to the diets was confirmed by randomly sampling participants to measure urinary tyrosol and hydroxytyrosol levels, using gas chromatography-mass spectrometry for virgin olive oil intake and measuring gamma-linolenic acid plasma content by gas chromatography for nut (walnut) intake.

Dr. Covas and her colleagues had reported that compared with the low-fat diet, the 2 Mediterranean diets produced beneficial changes in most cardiovascular risk factors and inflammatory markers at 3 months ( Table 2 ).[7]

The effects of the diets on oxidized LDL at 3 months were evaluated in a subgroup of 327 subjects. After adjustment for baseline values for each variable (Model 1), decreases in plasma levels of oxidized LDL were seen in each of the 2 Mediterranean groups (decrease was significant for the Mediterranean diet plus virgin olive oil), but no change was seen in the low-fat diet group ( Table 3 ). No significant changes were seen in activity of the antioxidant enzyme, glutathione peroxidase.

In a model adjusted for baseline values -- sex, age, center, basal weight and physical activity, smoking, diabetes, and LDL/high-density lipoprotein (HDL) cholesterol ratio (Model 2) -- oxidized LDL levels decreased in both Mediterranean diet groups, but only the change in oxidized LDL in the Mediterranean diet with virgin olive oil group again reached significance vs that of the low-fat diet group. Malondialdehyde in mononuclear cells, measured in 71 individuals, followed a similar pattern to oxidized LDL. No significant changes were seen in activity of the antioxidant enzyme glutathione peroxidase in any group after interventions.

As in the previous report from the study authors, a limitation of this study was that the nutritional education given to the enrollees on the low-fat diet was less intense than the education provided about the Mediterranean diets, Dr. Covas acknowledged.

PREDIMED is supported by the Spanish Ministry of Health (Fondo de Investigación Sanitaria) and Fundación Patrimonio Comunal Olivarero and Hojiblanca SA, California Walnut Commission, Borges SA, and Morella Nuts SA, which donated the olive oil, walnuts, almonds, and hazelnuts, respectively, used in the study.

Fruit and Vegetable Antioxidants Prevent Early Atherosclerosis Progression in Hamsters

Presenter: Thibault Sutra, PhD (University of Montpelier, Montpelier, France)

The antioxidants supplied in an extract of fruits and vegetables appear to prevent the progression of early atherosclerosis in hypercholesterolemic hamsters, according to a study reported by Dr. Sutra[8] and published simultaneously in the Journal of Agricultural and Food Chemistry.[9] Dr. Sutra and his colleagues believe that nicotinamide-adenine dinucleotide phosphate-oxidase complex (NADPH oxidase) can be modulated by dietary antioxidants. Development of atherosclerosis is thought to be closely dependent on increased oxidative stress, ie, an imbalance between reactive oxygen species (ROS) generation (superoxide anions, hydrogen peroxide, hydroxyl radicals) and natural cell antioxidant capacity, and the NADPH oxidase system is believed to be the major source of ROS in the vascular wall and in vascular smooth muscle cells.

This study was designed to trigger an arterial wall response to such an oxidative stress (fatty streak formation and aortic atherosclerosis emergence) in Golden Syrian hamsters. Few studies have investigated the effect of plant material on atherosclerosis and oxidative stress in rodents, and these studies were only focused on the effects of vegetables, Dr. Sutra noted, and the investigators believe, that this is the first study in which modulation of oxidative stress parameters, including cardiac production of superoxide anions and NADPH oxidase expression, was measured.

Golden Syrian hamsters have a plasma lipoprotein distribution similar to that of humans, and LDL is the major plasma cholesterol carrier. When these hamsters are fed a fat-rich diet they develop dyslipidemia and atherosclerotic plaques, similar in many respects to human atheroma. In this study, oxidative stress was induced by feeding the animals an atherogenic high-cholesterol and high-fat diet deficient in vitamins C and E and in selenium.

Two groups of 18 hamsters were fed the atherogenic diet by gavage for 12 weeks. One group received tap water and the other group received a solution of a commercial fruit and vegetable extract, Oxxynea (NB Consulting, Béziers, France). According to the manufacturer, powdered Oxxynea extract is obtained from 22 varieties of antioxidant-rich fruits and vegetables, including apples, asparagus, bilberry, apricots, black currants, broccoli, carrots, cherries, cucumbers, garlic, grapefruit, green cabbage, olives, onions, oranges, papaya, pineapple, red and white grapes, strawberries, tea, tomatoes, and wheat germ. Oxxynea also contains high level of catechins and low levels of other phenolic compounds, including gallic acid and anthocyanins, and lycopene and vitamin C were also identified. The weight of Oxxynea fed to the hamsters was calculated as equivalent to feeding 10 servings of fruits and vegetables per day in a human (approximately 800 g/day).

After 84 days, total cholesterol in the hamsters given Oxxynea was significantly reduced by 11.7% and non-HDL cholesterol by 14%, but HDL cholesterol was not changed compared with controls. The atherogenic index (total cholesterol/HDL cholesterol) was lowered by 8.3% in the hamsters receiving Oxxynea (P =01), and conversely, the plasma antioxidant capacity (measured by Trolox assay) was significantly increased. The hamsters that received Oxxynea also showed a marked 45% reduction in cardiac production of superoxide anion (P <0001), and area of aortic fatty streak accumulation was reduced by 77% (P =001).

Dr. Sutra and his colleagues believe that it is possible that the vitamin V, vitamin E, carotenoids, selenium, and polyphenols in the Oxxynea fruit and vegetable extract could have acted additively or perhaps synergistically to prevent atherosclerosis in this hamster model. They also speculated that polyphenol may play a specific role in vascular tissue mediated by NADPH oxidase.


Table 1. Carotid Intima-Media Thickness (CIMT) and Flow-Mediated Dilation (FMD) After 3.9 Years


  Placebo Vitamins P value
CIMT (mm) 0.83 ± 0.18 0.84 ± 0.17 .74
FMD (%) 3.0 (0.6-6.6) 4.0 (0.9-7.2) .48

 

Table 2. Changes in Cardiovascular Risk Factors and Inflammatory Markers at 3 Months


  Mediterranean Diet With Olive Oil vs Low-Fat Diet Mediterranean Diet With Nuts vs Low-Fat Diet
Mean (95% CI) P Value Mean (95% CI) P Value
Cardiovascular risk factors:
   SBP (mmHg) -5.9 (-8.7, -3.1) <001 -7.1 (-10.0, -4.1) <001
   DBP (mmHg) -1.60 (-3.00, -0.01) .048 -2.6 (-4.2, 1.0) .001
   Fasting glucose (mmol/) -0.39 (-0.72, -0.07) 0.17 -0.30 (-0.58, -0.01) .039
   Cholesterol-HDL/cholesterol ratio (mmol/L) -0.38 (-0.55, -022) <001 -0.26 (-0.42, -0.10) .002
Inflammatory markers:
   Interleukin-6 (ng/L) -1.6 (-2.5, -0.6) <003 -1.3 (-2.3, -0.4) <018
   ICAM-1 (ng/mL) -104 (-135, -72) <003 -97 (-128, -65) <003
   VCAM-1 (ng/mL) -178 (-277, -79) <003 -167 (-267, -68) <003

95% CI = 95% confidence interval; SBP = systolic blood pressure; DB = diastolic blood pressure; HDL = high-density lipoprotein; ICAM-1 = intercellular adhesion molecule-1; VCAM-1 = vascular cell adhesion molecule-1

 

Table 3. Crude and Adjusted 3-Month Changes in In Vivo Oxidized LDL and Glutathione Peroxidase (GSH-Px)


  Traditional Mediterranean Diet Low-Fat Diet P Value
+ Virgin Olive Oil + Nuts
Model 1
   Oxidized LDL (U/L) -10.1 (-15, -5) -7.5 (-12, -3) -2.6 (-8, 3) .043*
   GSH-Px (U/L) -16 (-45, 12) -10 (-36, 15) -20 (-50, 10) NS
Model 2
   Oxidized LDL (U/L) -10.6 (-14, -8) 7.3 (-11, -3) -2.9 (-7, 1) .017*
   GSH-Px (U/L) -16 (-45, 12) -10 (-36, 15) -20 (-50, 10) NS

*Mediterranean diet with virgin olive oil group vs low-fat diet group
GSH-Px = glutathione peroxidase; LDL = low-density lipoprotein; NS = not significant

 

Table 4. Plasma Lipid Concentration and Plasma Antioxidant Capacity


Group Atherogenic Diet Atherogenic Diet + Fruit and Vegetable Extract P Value
Total cholesterol 9.54 ± 0.20 8.42 + 0.16 <0001
HDL cholesterol 6.01 ± 0.27 5.9 ± 0.16 NS
Non-HDL cholesterol 3.12 ± 0.15 2.68 ± 0.17 .0066
Plasma antioxidant capacity 1.29 ± 0.06 1.42 ± 0.1 .0244

All values are millimoles per liter, means ± standard error of the mean; NS = not significant
HDL = high-density lipoprotein; LDL = low-density lipoprotein

 



References

  1. Potter K, Hankey GJ, Green DJ, et al. Long-term treatment with folic acid, vitamin B6 and B12 does not improve vascular structure or function: a randomized controlled trial. Atherosclerosis. 2007;8:1.  WO1-OR-6.
  2. The VITATOPS (Vitamins to Prevent Stroke) Trial: rationale and design of an international, large, simple, randomised trial of homocysteine-lowering multivitamin therapy in patients with recent transient ischaemic attack or stroke. Cerebrovasc Dis. 2002;13:120-126.
  3. Covas M-I, Corella D, Estruch R, et al. Effect of a traditional Mediterranean diet on lipoprotein oxidation: a randomized, controlled trial. Atherosclerosis. 2007;8:1.  WO1-OR-5.
  4. Panagiotakos DB, Pitsavos C, Chrysohoou C, et al. Status and management of blood lipids in Greek adults and their relation to sociodemographic, lifestyle and dietary factors: the ATTICA Study. Blood lipids distribution in Greece. Atherosclerosis. 2004;173:353-361.
  5. Lapointe A, Goulet J, Couillard C, et al. A nutritional intervention promoting the Mediterranean food pattern is associated with a decrease in circulating oxidized LDL particles in healthy women from the Quebec City Metropolitan Area. J Nutr. 2005;135:410-415.
  6. Krauss RM, Eckel RH, Howard B, et al. AHA Dietary Guidelines: revision 2000: a statement for healthcare professionals from the Nutrition Committee of the American Heart Association. Circulation. 2000;102:2284-2299.
  7. Estruch R, Martinez-Gonzalez MA, Corella D, et al; PREDIMED Study Investigators. Effects of a Mediterranean-style diet on cardiovascular risk factors: a randomized trial. Ann Intern Med. 2006;145:1-11.
  8. Sutra T, Decorde K, Cristol JP, et al. Oxidative stress in diet-induced atherosclerosis is concomitant with overexpression of NADPH oxidase: benefit of dietary antioxidants in Golden Syrian hamster. Atherosclerosis. 2007;8:1.  WO1-OR-4.
  9. Sutra T, Decorde K, Riss J, et al. A commercial extract of fruits and vegetables, Oxxynea, acts as a powerful antiatherosclerotic supplement in an animal model by reducing cholesterolemia, oxidative stress, and NADPH oxidase expression. J Agric Food Chem. 2007;55:4258-4263.

Linda Brookes, MSc, freelance medical writer based in London and New York

Disclosure: Linda Brookes, MSc, has disclosed no relevant financial relationships.