Novel risk factors for coronary heart disease: emerging connections

Nutrient intake, serum lipids and iron status of colligiate rugby players

Background

There are two main playing positions in rugby (backs and forwards), which demonstrate different exercise patterns, roles, and physical characteristics. The purpose of this study was: 1) to collect baseline data on nutrient intake in order to advise the athletes about nutrition practices that might enhance performance, and 2) to compare serum lipids, lipoproteins, apolipoproteins (apo), lecithin:cholesterol acyltransferase (LCAT) activity, and iron status of forwards and backs.

Methods

The sporting group was divided into 18 forwards and 16 backs and were compared with 26 sedentary controls. Dietary information was obtained with a food frequency questionnaire.

Results

There were significant differences among the three groups. The forwards had the highest body weight, body mass index, percentage of body fat (calculated by sum of four skinfold thicknesses), as well as the highest lean body mass, followed by the backs and the control group. The mean carbohydrate intake was marginal and protein intake was lower than the respective recommended targets in all three groups. The mean intakes of calcium, magnesium, and vitamins A, B₁, B₂, and C were lower than the respective Japanese recommended dietary allowances or adequate dietary intakes for the rugby players. The forwards had significantly lower high-density lipoprotein cholesterol (HDL-C) and HDL₂-C than the backs and had significantly higher apo B and LCAT activity than the controls. The backs showed significantly higher HDL-C, HDL₃-C, low-density lipoprotein cholesterol, and apo A-I, and LCAT activity than the controls. Four forwards (22%), five backs (31%), and three controls (12%) had hemolysis. None of the rugby players had anemia or iron depletion.

Conclusion

The findings of our study indicate that as the athletes increased their carbohydrate and protein intake, their performance and lean body mass increased. Further, to increase mineral and vitamin intakes, we recommended athletes increase their consumption of green and other vegetables, milk and dairy products, and fruits. The forwards showed more atherogenic lipid profiles than the backs, whereas the backs showed not only anti-atherogenic lipid profile, but also showed more atherogenic lipid profile relative to the control group. Additionally, our study showed none of the rugby players experienced anemia and/or iron depletion.

The therapeutic modulation of atherogenic dyslipidemia and inflammatory markers in the metabolic syndrome: what is the clinical relevance?

The metabolic syndrome consists of a constellation of clinical and biochemical risk factors that cluster together and heighten the risk for atherogenesis, cardiovascular diseases, and diabetes. Established risk cardiovascular factors like hypertension, atherogenic dyslipidaemia, and glucose intolerance occur in the setting of insulin resistance and central adiposity, with genetic and environmental influences modulating the ultimate risk. Chronic insults to the endothelium take its toll in the form of silent as well as clinically evident cardiovascular events. The cellular and vascular accompaniments have shed some light into the underlying pathophysiology. Heightened, low-grade inflammatory processes as well as a continuum of vascular insults ranging from early endothelial derangements to advanced atherosclerosis have been examined. In recent years there has been an explosion of basic and clinical knowledge related to the metabolic syndrome. Although dyslipidaemia is considered a traditional risk component for the syndrome, its qualitative aspects, genetically determined subfractions, and variation in proatherogenic tendency have generated renewed interest and debate. New targets within the dyslipidaemic spectrum that have differing clinical relevance are being evaluated. The effect of heredity, lifestyle changes, pharmacotherapeutic agents, and supplements is being investigated. Further research into the impact of dyslipidemia and inflammation as both pathophysiologic risk factors and objects for targeted therapy in the metabolic syndrome should deepen our understanding and unravel answers to the underlying dynamics in this global epidemic.

Major coronary risk factors and death from coronary heart disease: baseline and follow-up mortality data from the Second National Health and Nutrition Examination Survey (NHANES II)

BACKGROUND

Although the major risk factors for coronary heart disease (CHD) are well-established, intense efforts persist in the search for "novel" or "emerging" risk factors because of the notion that as many as half of CHD victims may not have the traditional risk factors.

OBJECTIVE

Compare prevalences of major risk factors among persons with fatal CHD in a nationally representative population sample.

METHODS

Baseline data from the Second National Health and Nutrition Examination Survey and 17-year follow-up mortality data were examined for 8,069 adults (3,701 men; 4,368 women) aged 30 to 75 years in 1976-1980. We calculated sex-specific prevalences of hypertension, elevated total cholesterol (> or = 240 mg/dL), cigarette smoking, and the presence of at least one of these three major risk factors. The relative risk of death from CHD associated with the three major risk factors was calculated in sex-specific multivariable models adjusted for age, race, and education.

RESULTS

Overall, nearly 75% of US adults had at least one of the three major risk factors. Those who died of CHD, compared to those who did not die of CHD, had respectively, greater prevalences of hypertension (men: 48% vs. 38%; women: 76% vs. 33%). Similarly, persons who had fatal CHD were more likely to have elevated total cholesterol (men: 53% vs. 30%; women: 55% vs. 34%), although the finding was not statistically significant in women. Smoking prevalence was also greater among persons who died of CHD than those who did not for both men (64% vs. 40%) and women (43% vs. 33%). The proportion of persons with at least one of the three major risk factors was significantly (P < or = 0.01) greater among those who died from CHD compared with those who did not (men: 92% vs. 74%; women: 98% vs. 70%). The risk of fatal CHD was 51% lower among men and 71% lower among women with none of the 3 risk factors compared to those with at least one. Had all three major risk factors not occurred, 64% of all CHD deaths among women and 45% of all CHD deaths among men could have been avoided.

CONCLUSIONS

Nine out of ten US adults who died of CHD had at least one of the three major established risk factors. Thus, the notion that many CHD victims do not have the traditional risk factors is a misconception. Policies and strategies that increase the prevalence of a low risk profile are needed, and aggressive efforts in the prevention and control of the major established risk factors remain the key to continued reductions in CHD mortality.

Novel cardiovascular risk factors

In addition to the well-established cardiovascular risk factors of elevated total and low-density lipoprotein cholesterol, hypertension, and cigarette smoking, multiple additional factors are suspected culprits in both the development and progression of atherothrombosis. It is key for the clinician to critically review research findings utilizing an organized framework in order to credibly advise the patient with cardiovascular disease or at risk for its development. The current evidence and recommendations regarding the following "novel"or "emerging" risk factors will be reviewed: lipoprotein(a), hyperhomocysteinemia, C-reactive protein, infectious processes, fibrinogen, and microalbuminuria.

Lipoprotein(a): an emerging cardiovascular risk factor

Lipoprotein(a) is a cholesterol-enriched lipoprotein, consisting of a covalent linkage joining the unique and highly polymorphic apolipoprotein(a) to apolipoprotein B100, the main protein moiety of low-density lipoproteins. Although the concentration of lipoprotein(a) in humans is mostly genetically determined, acquired disorders might influence synthesis and catabolism of the particle. Raised concentration of lipoprotein(a) has been acknowledged as a leading inherited risk factor for both premature and advanced atherosclerosis at different vascular sites. The strong structural homologies with plasminogen and low-density lipoproteins suggest that lipoprotein(a) might represent the ideal bridge between the fields of atherosclerosis and thrombosis in the pathogenesis of vascular occlusive disorders. Unfortunately, the exact mechanisms by which lipoprotein(a) promotes, accelerates, and complicates atherosclerosis are only partially understood. In some clinical settings, such as in patients at exceptionally low risk for cardiovascular disease, the potential regenerative and antineoplastic properties of lipoprotein(a) might paradoxically counterbalance its athero-thrombogenicity, as attested by the compatibility between raised plasma lipoprotein(a) levels and longevity.

The iron hypothesis of atherosclerosis and its clinical impact

The iron hypothesis as an alternative explanation for the gender difference in the incidence and mortality of atherosclerosis has provoked increased debates and public health concerns. In this review we summarize the historical and recent literature on the iron hypothesis and discuss several related clinical issues and their implications. Apart from misconstruction of study populations, lack of a good method to reflect the iron contents of tissues may be the major factor for causing inconsistent results from epidemiological studies. Published data from 11 countries clearly indicate that the mortality from cardiovascular diseases is correlated with liver iron. We propose that redox-active iron in tissue is the atherogenic portion of total iron stores. Recently developed magnetic resonance imaging techniques in combination with Fe chelators may allow future studies to examine this component of body iron in lesions and the whole body. Several clinical situations characterized by increased iron stores have been proposed as 'human models' suitable for further tests of the iron hypothesis. Patients with end-stage renal disease may be the most unique cohort, having significant increases in their iron stores, low-density lipoprotein (LDL) oxidation, and cardiovascular events. Other patient groups may be well suited for specific studies of different atherogenic events. With a better understanding of iron-driven oxidative damage, well controlled and effectively designed studies on these models will finally bring us to the truth of the iron hypothesis.