Antioxidant strategy for cardiovascular diseases

Assessing causal links between age at menarche and adolescent mental health: a Mendelian randomisation study

BACKGROUND

The timing of puberty may have an important impact on adolescent mental health. In particular, earlier age at menarche has been associated with elevated rates of depression in adolescents. Previous research suggests that this relationship may be causal, but replication and an investigation of whether this effect extends to other mental health domains is warranted.

METHODS

In this Registered Report, we triangulated evidence from different causal inference methods using a new wave of data (N = 13,398) from the Norwegian Mother, Father, and Child Cohort Study. We combined multiple regression, one- and two-sample Mendelian randomisation (MR), and negative control analyses (using pre-pubertal symptoms as outcomes) to assess the causal links between age at menarche and different domains of adolescent mental health.

RESULTS

Our results supported the hypothesis that earlier age at menarche is associated with elevated depressive symptoms in early adolescence based on multiple regression (β =  - 0.11, 95% CI [- 0.12, - 0.09], pone-tailed < 0.01). One-sample MR analyses suggested that this relationship may be causal (β =  - 0.07, 95% CI [- 0.13, 0.00], pone-tailed = 0.03), but the effect was small, corresponding to just a 0.06 standard deviation increase in depressive symptoms with each earlier year of menarche. There was also some evidence of a causal relationship with depression diagnoses during adolescence based on one-sample MR (OR = 0.74, 95% CI [0.54, 1.01], pone-tailed = 0.03), corresponding to a 29% increase in the odds of receiving a depression diagnosis with each earlier year of menarche. Negative control and two-sample MR sensitivity analyses were broadly consistent with this pattern of results. Multivariable MR analyses accounting for the genetic overlap between age at menarche and childhood body size provided some evidence of confounding. Meanwhile, we found little consistent evidence of effects on other domains of mental health after accounting for co-occurring depression and other confounding.

CONCLUSIONS

We found evidence that age at menarche affected diagnoses of adolescent depression, but not other domains of mental health. Our findings suggest that earlier age at menarche is linked to problems in specific domains rather than adolescent mental health in general.

Approaches to estimate bidirectional causal effects using Mendelian randomization with application to body mass index and fasting glucose

Mendelian randomization (MR) is an epidemiological framework using genetic variants as instrumental variables (IVs) to examine the causal effect of exposures on outcomes. Statistical methods based on unidirectional MR (UMR) are widely used to estimate the causal effects of exposures on outcomes in observational studies. To estimate the bidirectional causal effects between two phenotypes, investigators have naively applied UMR methods separately in each direction. However, bidirectional causal effects between two phenotypes create a feedback loop that biases the estimation when UMR methods are naively applied. To overcome this limitation, we proposed two novel approaches to estimate bidirectional causal effects using MR: BiRatio and BiLIML, which are extensions of the standard ratio, and limited information maximum likelihood (LIML) methods, respectively. We compared the performance of the two proposed methods with the naive application of UMR methods through extensive simulations of several scenarios involving varying numbers of strong and weak IVs. Our simulation results showed that when multiple strong IVs are used, the proposed methods provided accurate bidirectional causal effect estimation in terms of median absolute bias and relative median absolute bias. Furthermore, compared to the BiRatio method, the BiLIML method provided a more accurate estimation of causal effects when weak IVs were used. Therefore, based on our simulations, we concluded that the BiLIML should be used for bidirectional causal effect estimation. We applied the proposed methods to investigate the potential bidirectional relationship between obesity and diabetes using the data from the Multi-Ethnic Study of Atherosclerosis cohort. We used body mass index (BMI) and fasting glucose (FG) as measures of obesity and type 2 diabetes, respectively. Our results from the BiLIML method revealed the bidirectional causal relationship between BMI and FG in across all racial populations. Specifically, in the White/Caucasian population, a 1 kg/m2 increase in BMI increased FG by 0.70 mg/dL (95% confidence interval [CI]: 0.3517-1.0489; p = 8.43×10-5), and 1 mg/dL increase in FG increased BMI by 0.10 kg/m2 (95% CI: 0.0441-0.1640; p = 6.79×10-4). Our study provides novel findings and quantifies the effect sizes of the bidirectional causal relationship between BMI and FG. However, further studies are needed to understand the biological and functional mechanisms underlying the bidirectional pathway.

Mendelian randomization analysis of a time-varying exposure for binary disease outcomes using functional data analysis methods

A Mendelian randomization (MR) analysis is performed to analyze the causal effect of an exposure variable on a disease outcome in observational studies, by using genetic variants that affect the disease outcome only through the exposure variable. This method has recently gained popularity among epidemiologists given the success of genetic association studies. Many exposure variables of interest in epidemiological studies are time varying, for example, body mass index (BMI). Although longitudinal data have been collected in many cohort studies, current MR studies only use one measurement of a time-varying exposure variable, which cannot adequately capture the long-term time-varying information. We propose using the functional principal component analysis method to recover the underlying individual trajectory of the time-varying exposure from the sparsely and irregularly observed longitudinal data, and then conduct MR analysis using the recovered curves. We further propose two MR analysis methods. The first assumes a cumulative effect of the time-varying exposure variable on the disease risk, while the second assumes a time-varying genetic effect and employs functional regression models. We focus on statistical testing for a causal effect. Our simulation studies mimicking the real data show that the proposed functional data analysis based methods incorporating longitudinal data have substantial power gains compared to standard MR analysis using only one measurement. We used the Framingham Heart Study data to demonstrate the promising performance of the new methods as well as inconsistent results produced by the standard MR analysis that relies on a single measurement of the exposure at some arbitrary time point.

Clinical Strategies for Managing Dyslipidemias

Dyslipidemia is defined as elevated fasting blood levels of total cholesterol (TC), and its primary lipoprotein carrier—low-density lipoprotein (LDL), triglycerides (TG), or reduced high-density lipoprotein (HDL), alone, or in combination (mixed dyslipidemia). Dyslipidemia is well known to be associated with cardiovascular disease (CVD) risk. All patients with dyslipidemia should initiate therapeutic lifestyle changes to target lifestyle-related factors such as physical inactivity, dietary habits, and obesity. The combination of a proper dietary plan and regular aerobic exercise has been reported to lower TC, LDL-C, and TG by 7% to 18%, while increasing HDL-C by 2% to 18%. Numerous pharmacological therapies are available and aggressive therapy using a HMG-CoA reductase (3-hydroxy-3-methyl-glutaryl coenzyme A reductase) inhibitor (statins) should be initiated if lifestyle therapy is not enough to achieve optimal lipid levels with a primary target of lowering LDL-C levels. Aggressive treatment of dyslipidemia with maximal dosage of statin drugs have been reported to reduce LDL-C by 30% to 60%. If mixed dyslipidemia is present, a combination therapy with statin, niacin, cholestyramine, or fibrates should be initiated to reduce the risk of CVD events. These strategies have been shown to reduce CVD risk and optimize LDL-C levels in primary and secondary prevention of CVD.

Dyslipidemia and Risk of Coronary Heart Disease: Role of Lifestyle Approaches for Its Management

Multiple risk factors have a causative relationship to the etiology of coronary heart disease (CHD). However, it is clear that dyslipidemia plays a central role. The chain of evidence is strongest for elevated levels of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C). An inverse association has also been demonstrated between levels of high-density lipoprotein cholesterol (HDL-C) and its principal apolipoprotein, A-1, and risk of CHD. Elevated levels of fasting triglyceride (TG) also are a predictor of CHD, but the independent contribution of TG is difficult to prove because of its usual association with reduced levels of HDL-C; elevated levels of small, dense, highly-atherogenic LDL particles; and the metabolic syndrome. Elevated fasting levels of non—HDL-C (TC — LDL-C) and apolipoprotein B also are strongly predictive of the risk of CHD. Therapeutic lifestyle changes are important adjuncts to pharmacologic management of dyslipidemia. The purpose of this article is to review these contributions with an emphasis on dietary habits (particularly lipid intake), weight management, and aerobic exercise.

Role of oxidants and antioxidants in atherosclerosis: results of in vitro and in vivo investigations

Both in vitro and in vivo studies have shown that oxidants are central in the development of atherosclerosis. Consequently, additional studies evaluated the protective effects of various natural and synthetic antioxidants, alone and in combination, with most studies focusing on alpha-tocopherol (vitamin E). Here, we summarize the role of oxidants in the pathomechanism of atherosclerosis. We also discuss epidemiological studies and others focused on the protective effect of vitamin E against atherosclerosis. Other antioxidants are also considered if they were included in studies involving vitamin E. The protective effect of antioxidants on atherosclerotic pathomechanisms has been confirmed in vitro, but only in some animal studies. Various epidemiological and observational studies have produced conflicting results on the protective effect of antioxidants. Most studies of primary or secondary prevention failed to show a protective effect. These conflicting results are biased by a number of factors, including differences between the study groups. Therefore, we describe these studies in detail.

Adverse effects of vitamin E by induction of drug metabolism

Observational studies with healthy persons demonstrated an inverse association of vitamin E with the risk of coronary heart disease or cancer, the outcome of large-scale clinical trials conducted to prove a benefit of vitamin E in the recurrence and/or progression of such disease, however, was disappointing. Vitamin E did not provide benefits to patients with cardiovascular diseases, cancer, diabetes or hypertension. Even harmful events and worsening of pre-existing diseases were reported, which are hard to explain. Since vitamin E is metabolized along the same routes as xenobiotics and induces drug-metabolizing enzymes in rodents, it is hypothesized that a supplementation with high dosages of vitamin E may also lead to an induction of the drug-metabolizing system in patients that depend on drug therapy. Compromising essential therapy might therefore outweigh any benefit of vitamin E in patients. It is recommended to work out at which threshold the drug-metabolizing system can be induced in humans before new trials with high dosages of vitamin E are started.

Diet in childhood and adult cardiovascular and all cause mortality: the Boyd Orr cohort

OBJECTIVE

To examine the association between childhood diet and cardiovascular mortality.

DESIGN

Historical cohort study.

SETTING

16 centres in England and Scotland.

PARTICIPANTS

4028 people (from 1234 families) who took part in Boyd Orr's survey of family diet and health in Britain between 1937 and 1939 followed up through the National Health Service central register. EXPOSURES STUDIED: Childhood intake of fruit, vegetables, fish, oily fish, total fat, saturated fat, carotene, vitamin C, and vitamin E estimated from household dietary intake.

MAIN OUTCOME MEASURES

Deaths from all causes and deaths attributed to coronary heart disease and stroke.

RESULTS

Higher childhood intake of vegetables was associated with lower risk of stroke. After controlling for age, sex, energy intake, and a range of socioeconomic and other confounders the rate ratio between the highest and lowest quartiles of intake was 0.40 (95% confidence interval 0.19 to 0.83, p for trend 0.01). Higher intake of fish was associated with higher risk of stroke. The fully adjusted rate ratio between the highest and lowest quartile of fish intake was 2.01 (95% confidence interval 1.09 to 3.69, p for trend 0.01). Intake of any of the foods and constituents considered was not associated with coronary mortality.

CONCLUSIONS

Aspects of childhood diet, but not antioxidant intake, may affect adult cardiovascular risk.

Childhood and adult dietary vitamin E intake and cardiovascular risk factors in mid-life in the 1946 British Birth Cohort

OBJECTIVES

To determine whether dietary vitamin E intake in childhood or mid-life was predictive of adult hypertension and high waist circumference, as two important risk factors for cardiovascular disease.

DESIGN

Longitudinal study of a social class stratified random sample of all the legitimate, singleton births in the week of 3-9 March 1946.

SETTINGS

England, Scotland and Wales.

SUBJECTS

The 2980 survey members who provided information on diet, health and sociodemographic information at two time points; age 4 y in 1950 (24-h dietary recall) and 43 y in 1989 (48-h dietary recall).

MAIN OUTCOME MEASURES

Outcomes were adjusted odds ratios (ORs) for hypertension and high waist circumference at age 43 y by thirds of vitamin E intake, relative to the highest intake thirds at both ages.

RESULTS

The lowest consumers of vitamin E in both childhood and adulthood were more likely to be hypertensive (OR 1.8, 95% confidence interval (CI): 1.03-3.08) and have high waist circumference (OR 1.6, 95% CI: 1.02-2.43) than those consuming high levels at both ages. A low intake of vitamin E at just one time point was not associated with a statistically significant increased risk of hypertension or high waist circumference. Social class was also an independent and equally strong predictor of these coronary risk factors, indicating that the relation between social class and cardiovascular risks was not mediated solely by the current measures of diet and lifestyle.

CONCLUSIONS

Unique data on vitamin E intake from foods in both childhood and adulthood have indicated that relatively low intake of vitamin E at both ages predicted hypertension and high waist circumference at age 43 y.

'Mendelian randomization': can genetic epidemiology contribute to understanding environmental determinants of disease?

Associations between modifiable exposures and disease seen in observational epidemiology are sometimes confounded and thus misleading, despite our best efforts to improve the design and analysis of studies. Mendelian randomization-the random assortment of genes from parents to offspring that occurs during gamete formation and conception-provides one method for assessing the causal nature of some environmental exposures. The association between a disease and a polymorphism that mimics the biological link between a proposed exposure and disease is not generally susceptible to the reverse causation or confounding that may distort interpretations of conventional observational studies. Several examples where the phenotypic effects of polymorphisms are well documented provide encouraging evidence of the explanatory power of Mendelian randomization and are described. The limitations of the approach include confounding by polymorphisms in linkage disequilibrium with the polymorphism under study, that polymorphisms may have several phenotypic effects associated with disease, the lack of suitable polymorphisms for studying modifiable exposures of interest, and canalization-the buffering of the effects of genetic variation during development. Nevertheless, Mendelian randomization provides new opportunities to test causality and demonstrates how investment in the human genome project may contribute to understanding and preventing the adverse effects on human health of modifiable exposures.

Long-term vitamin E supplementation fails to reduce lipid peroxidation in people at cardiovascular risk: analysis of underlying factors

BACKGROUND: Antioxidant supplementation with vitamin E had no effect in the prevention of cardiovascular diseases (CVD) in three recent large, randomized clinical trials. In order to reassess critically the role of vitamin E in CVD prevention, it is important to establish whether these results are related to a lack of antioxidant action. METHODS: We examined the in vivo antioxidant effect of vitamin E (300 mg/day for about three years) in 144 participants in the Primary Prevention Project (females and males, aged >/= 50 y, with at least one major CV risk factor, but no history of CVD). Urinary 8-epi-PGF2alpha (isoprostane F2alpha-III or 15-F2t-isoP), a validated biomarker of lipid peroxidation, was measured by mass spectrometry. RESULTS: Urinary excretion of 8-epi-PGF2alpha [pg/mg creatinine, median (range)] was 141 (67-498) in treated and 148 (76-561) in untreated subjects (p = 0.10). Taking into account possible confounding variables, multiple regression analysis confirmed that vitamin E had no significant effect on this biomarker. Levels of 8-epi-PGF2alpha were in the normal range for most subjects, except smokers and those with uncontrolled blood pressure or hyperglycemia. CONCLUSIONS: Prolonged vitamin E supplementation did not reduce lipid peroxidation in subjects with major cardiovascular risk factors. The observation that the rate of lipid peroxidation was near normal in a large proportion of subjects may help explain why vitamin E was not effective as an antioxidant in the PPP study and was ineffective for CVD prevention in large scale trials.

Nutraceuticals: vitamins and other nutrients in coronary heart disease

Nutraceuticals and specifically vitamins, oils and herbs are increasingly being taken by patients. Some supplements may improve cardiovascular outcome, most are unproved, and some could potentially cause harm. Marine lipid supplementation needs to be considered in all patients who have manifest coronary heart disease. For most supplements more data are needed before confident recommendations can be made.