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A Happy Trio of Hearty Fish Findings
7/9/2007
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Three new studies add heartening support to diets rich in fruits, nuts, vegetables, and fish

by Craig Weatherby



Rhythmic benefits of omega-3s aren't quite universal

The only known exceptions to the benefit of ingesting ample amounts of omega-3s are people with congestive heart failure and/or implanted cardiac defibrillators.

These folks’ dangerously few functional heart cells are starved for blood flow, which makes them “hyper-excitable” and prone to trigger the arrhythmias that cause most cases of sudden cardiac death.

Omega-3s selectively quiet hyper-excitable cells, bringing anti-arrhythmia benefits to most heart patients... and to the many outwardly healthy people who die from unexpected arrhythmias daily.

However, taking omega-3 fish oil or even eating fatty fish can represent a risk to people with congestive heart failure or implanted cardiac defibrillators, because dietary omega-3s could suppress pumping action in their hearts’ hyper-excitable cells, which account for an unusually large proportion of their blood-pumping power.

Research results reported over the past few weeks have been very good for the reputation of fish as heart-healthy fare,thanks to their uniquely abundant portions of omega-3s and vitamin D.


Let’s take a quick look at the happy findings, which hail from labs in Spain, Greece, and southern California.


"Green" Mediterranean Diet keeps arteries clearer

It's become increasingly clear that high cholesterol levels don’t necessarily present cardiac risks. In fact, about half of all people who die from heart problems have perfectly healthy cholesterol profiles, while many people with very high levels show no signs of clogged arteries.


Instead, a growing sicentific consensus holds that inflammationwhich makes blood sticky, oxidizes cholesterol, and creates rigid, clogged arteries and thereby starves heart muscle and promotes unstable heart rhythmsis the strongest driver of cardiac risks.


Rather than being primary cardiac problems, high LDL cholesterol and low HDL cholesterol seem to act as added risk factors, with the statin drugs used to lower LDL levels doing as much or more good because they reduce inflammation quite effectively.


A new study finds that the idealized Mediterranean Diet that includes ample fish helps prevent oxidation of LDL (“Bad”) cholesterol: a process driven largely by stress, inactivity, poor diets, and resulting "silent" inflammation.


We should note that when researchers use the term “Mediterranean Diet” they refer to an idealized version of traditional Italian, Spanish, and Greek cuisines.


The idealized Mediterranean Diet is richer in fruit, vegetables and fish than is the dietary reality in most areas of these sunny southern European countries, where red/cured meats and refined flour products play bigger-than-ideal parts.


Oxidation of LDL cholesterol promotes build up of arterial plaque, which causes atherosclerosis (hardening of the arteries), reduces blood flow, and can lead to heart 

attacks, congestive heart failure, and

Vitamin D: Ideal forms and sources

The term “vitamin D” actually refers to either of two forms: D3 (cholecalciferol) and D2 (ergocalciferol).

Vitamin D3, which is more “bio-active” and effective is found only in animal foods—especially fish, see—and is produced in skin exposed to solar UVB radiation.

Vitamin D2 is a less bio-active and beneficial form derived from plants, which contain small amounts.

However, vitamin D2 is cheaper than vitamin D3, so most dietary supplements contain vitamin D2. Unfortunately, most Americans get most of their vitamin D from supplements containing this sub-optimal form (Calvo MS et al 2005).

sudden cardiac death.


Conversely, "green" diets rich in colorful fruits and vegetablesyield higher antioxidant activity in the blood, which helps prevent oxidation of LDL cholesterol by free oxygen radicals and thereby reduces the progression of atherosclerosis.


Spanish researchers at Hospital Clinic in Barcelona recruited 372 people in poor cardiovascular health (162 men and 210 women, average age 67.8), and randomly assigned them to one of three diets for three months:

  • Standard European Diet adjusted to be low in total fat

  • Mediterranean Diet plus extra-virgin olive oil (Med+EV Olive Oil)

  • Mediterranean Diet plus nuts (Med+Nuts)

After three months, it was clear that the best results stemmed from eating the Mediterranean Diet plus extra-virgin olive oil (Fito M et al 2007).


Levels of oxidized LDL dropped by 10.6 units per liter among people in the Med+EV Olive Oil group, and dropped by 7.3 units per liter among the Med+Nuts group.


As the authors noted, “The present study is, to our knowledge, the first randomized controlled clinical trial focused on the effect of a Mediterranean type diet on in vivo LDL oxidation” (Fito M et al 2007).


Both Mediterranean-style diets resulted in beneficial decreases in blood pressure, while the Med+Nuts diet led to greater reductions in triglyceride levels and increases in blood levels of HDL (“good”) cholesterol, versus the Med+EV Olive Oil diet.


Greek study affirms ability of fish to stabilize heart rhythms

Back in 2005, we reported on early results from a large population study in Greece, called ATTICA, which showed that fish-rich diets lower blood levels of inflammation, thereby reducing a key risk factor for heart disease (See “Fish Inhibits Heart-Attacking Inflammation”).


Now the same research group reports findings that support the previously shown ability of fishy diets to reduce the risk of arrhythmias: the irregular heartbeats that cause about half of all heart-related deaths (Chrysohoou C et al 2007).


They sought to see whether diets rich in fish (hence also high in omega-3 fatty acids) would produce beneficial changes in electrical properties of the heart, as recorded by electrocardiogram tests.

The Greek scientists were looking for differences in something called “heart rate-corrected QT,” or QTc, which provides a measure of arrhythmia risk. Longer-lasting QTc is associated with higher risk.


During 2001 and 2002, they enrolled 1,514 men and 1,528 women (18-89 years old) from the Attica area of Greece.


The Greek doctors recorded participants’ demographic, lifestyle, dietary, and clinical characteristics and determining the volunteers’ dietary habits by using a food-intake survey.


They found that, compared with people who ate no fish, those who consumed more than 300 grams (10.7 ounces) of fish per week had average QTc-durations that were 13.6 percent lower, which indicates a relatively lower risk of arrhythmia.


These positive findings held even after the researchers adjusted the results to account for differences in age, sex, physical activity status, body mass index (BMI), smoking habits, intake of nuts, and other potential confounding factors.


Better yet, compared with people who ate no fish, the fish-lovers were 29.2 percent less likely to have QTc intervals greater than 0.45 seconds, which is a very desirable difference.


As the Greeks wrote, “fish intake seems to provide anti-arrhythmic protection...” (Chrysohoou C et al 2007)


Note: There is one exception to the rule that omega-3s are good for heart rhythms: see our sidebar titled “Rhythmic benefits of omega-3s not quite universal”.


Vitamin D linked to reduced risks of heart disease and diabetes
The reputation of vitamin D has been rising fast, and a new analysis of population data should send it soaring even higher.


Researchers at Charles R. Drew University of Medicine and Science in Los Angeles looked at data from the Third National Health and Nutrition Examination Survey (NHANES), which was conducted by the National Center for Health Statistics between January 1, 1988, and December 31, 1994 (Martins D et al 2007).


The researchers used data collected from 7,186 men and 7,902 women, with results that make vitamin D look awfully good for heart health.


The subjects had average vitamin D blood levels of 75 nmol/L (75 nanomoles per liter of blood).


Blood levels below 40 nmol/L are considered grossly inadequate and unhealthful, and a level of 80 nmol/L is considered sub-optimal (Lappe JM et al 2006).


The key finding was that blood levels of vitamin D were generally lower in people who suffered from hypertension (high blood pressure) or high blood triglyceride levels, or who were diabetic.

Lower-than-average vitamin D levels were also more common in women, the elderly, and racial or ethnic minorities.


As the authors wrote, “This is the first study, to our knowledge, to demonstrate a significant association between low vitamin D levels and CVD risk factors in a nationally representative sample. Previous studies suggesting similar associations between low serum [blood] vitamin D levels and CVD risk factors were limited to subpopulations and small study samples.”


The researchers reported that, compared with people with vitamin D levels of at least 92 nmol/L or higher, those with low levels of vitamin D (below 52 nmol/L) had higher rates of major health problems or risk factors for these conditions:

  • Hypertension (30 percent higher risk)

  • Diabetes mellitus (98 percent higher risk)

  • Obesity (1.29 higher risk)

  • High blood triglyceride levels (47 percent higher risk).

Of course, there could be other factors associated with higher intake of vitamin D, such as higher omega-3 intake, since fish are the richest sources of both nutrients. But the researchers attempted adjust the results for omega-3s and other known risk/benefit factors.


At minimum, the positive results of new analysis calls for more research into links between vitamin D levels – from sun exposure or dietary sources – and these major health conditions.


And as the researchers said, vitamin D blood levels higher than the highest recorded in this study population – that is, levels higher than 92 nmol/L – could well confer additional preventive-health benefits.


The authors made four key points about the inadequacy of current recommendations for the amount of food/supplement intake and sun exposure needed to ensure adequate blood levels (Martins D et al 2007; clarifying comments added in brackets):

  • “The data for the historical reference range for the circulating level of [vitamin D] originated from sun-deprived human populations with suboptimal vitamin D intake and may have underestimated the physiologic demands for vitamin D.”

  • “Recommended optimum levels of vitamin D have been established without accounting for the ubiquitous nature of the vitamin D receptor [throughout the body] and the possible salutary affects of vitamin D on other organ systems that may affect CVD [cardiovascular disease]. Indeed, even the adequacy of present recommendations for vitamin D to prevent osteomalacia [osteoporosis] has been questioned.”

  • “Vitamin D deficiency has been associated with congestive heart failure, whereas increased blood levels of [vitamin D] in response to UV-B irradiation [from sun exposure] have been associated with decreased BP [blood pressure].”

  • “Vitamin D may affect CVD [cardiovascular disease] and its risk factors through other pathways, such as its immunosuppressive effects to reduce the proliferation of lymphocytes [white blood cells] and the production of cytokines [pro-inflammatory messenger proteins], which have recently been identified as having an important role in atherogenesis [build up of arterial plaque].

In other words, the new results make sense in light of what’s already known about the effects of vitamin D on bodily risk factors for cardiovascular disease.


Experts believe that the evidence supports raising the safe upper limit for intake of vitamin D by a factor of five, from the current 2,000 IU per day to 10,000 IU per day (see “Review Supports Safety of Much Higher Vitamin D Intake”).



Sources

  • Fito M, Guxens M, Corella D, Saez G, Estruch R, de la Torre R, Frances F, Cabezas C, Lopez-Sabater Mdel C, Marrugat J, Garcia-Arellano A, Aros F, Ruiz-Gutierrez V, Ros E, Salas-Salvado J, Fiol M, Sola R, Covas MI; for the PREDIMED Study Investigators. Effect of a traditional Mediterranean diet on lipoprotein oxidation: a randomized controlled trial. Arch Intern Med. 2007 Jun 11;167(11):1195-203.

  • Chrysohoou C, Panagiotakos DB, Pitsavos C, Skoumas J, Krinos X, Chloptsios Y, Nikolaou V, Stefanadis C. Long-term fish consumption is associated with protection against arrhythmia in healthy persons in a Mediterranean region—the ATTICA study. Am J Clin Nutr. 2007 May;85(5):1385-91.

  • Martins D, Wolf M, Pan D, Zadshir A, Tareen N, Thadhani R, Felsenfeld A, Levine B, Mehrotra R, Norris K. Prevalence of cardiovascular risk factors and the serum levels of 25-hydroxyvitamin D in the United States: data from the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2007 Jun 11;167(11):1159-65.

  • Lappe JM, Davies KM, Travers-Gustafson D, Recker RR, Heaney RP. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. American Journal of Clinical Nutrition, Vol. 85, No. 6, 1586-1591, June 2007.

  • Calvo MS, Whiting SJ, Barton CN. Vitamin D intake: a global perspective of current status. J Nutr. 2005 Feb;135(2):310-6. Review.
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