Those confounded vitamins: what can we learn from the differences between observational versus randomised trial evidence?

Lawlor, Debbie A.; Smith, George Davey; Bruckdorfer, K. Richard; Kundu, Devi; Ebrahim, Shah

doi:10.1016/s0140-6736(04)16260-0

Cited by 404 publications

(278 citation statements)

References 20 publications

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“…Blood samples were analysed in this subsample to provide objective validation of effects established in the analysis of FFQ data for two antioxidant vitamins (C and E), and two mineral cofactors (selenium and copper) defined a priori to be of primary interest in the original study protocol. While we are unable to exclude the possibility of confounding by lifestyle factors (Lawlor et al, 2004), these observations warrant detailed consideration.…”

Section: Discussionmentioning

confidence: 74%

Lung function and blood levels of copper, selenium, vitamin C and vitamin E in the general population

et al. 2005

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Background: Increased dietary intake of antioxidants has been associated with higher lung function, but few studies have used biological markers of antioxidant intake. Objective: This study aimed to determine if antioxidant status, as measured by blood levels, influences lung function. Design: Using a random subsample of 479 participants, aged 18-65 y old, from a larger cross-sectional observational study, the association of forced expiratory volume in 1 s (FEV 1 ) with plasma copper, vitamin C, vitamin E and serum selenium was assessed. Results: An s.d. increase in blood copper level was associated with a difference in FEV 1 of À48 ml (95% confidence intervals: À95, À2 ml, P ¼ 0.04), vitamin C þ 49 ml ( þ 4, þ 94, P ¼ 0.03), vitamin E À15 ml (À62, þ 32, P ¼ 0.53) and selenium þ 52 ml ( þ 7, þ 96, P ¼ 0.02). The sizes of association were not appreciably altered in a mutually adjusted model. Conclusions: Higher levels of serum vitamin C and selenium appear to be associated with higher FEV 1 . The association between higher serum copper and lower FEV 1 requires further study in view of the ubiquitous exposure to this mineral. Sponsorship: National Asthma Campaign and British Lung Foundation.

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Section: Discussionmentioning

confidence: 74%

Lung function and blood levels of copper, selenium, vitamin C and vitamin E in the general population

et al. 2005

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“…For example, there have been many claims about the benefits of various vitamin supplements based on observational studies 128,129 that have been reliably refuted by large-scale randomized trials. [130][131][132] Similarly, when compared with the results from randomized trials of the effects of treatments for several different cancers, observational studies have generated improbable results despite controlling for comorbidity, extent of disease and many other characteristics that were recorded in detailed databases [133][134][135] (as is also the case for reported associations of statins with lower rates of cancer 90,[136][137][138] ). These findings are consistent with empirical studies in which biases in observational studies were shown to be large enough to conclude falsely that treatment produced benefit or harm, with none of a range of statistical strategies (such as regression analysis or propensity matching) capable of adjusting adequately or predictably for bias.…”

Section: Biases Due To Differences In Underlying Risks Of Health Outcmentioning

confidence: 99%

Interpretation of the evidence for the efficacy and safety of statin therapy

et al. 2016

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms SummaryThis review is intended to help clinicians, patients and the public make informed decisions about statin therapy for the prevention of heart attacks and strokes. It explains how the evidence that is available from randomized controlled trials yields reliable information about both the efficacy and safety of statin therapy. In addition, it discusses how claims that statins commonly cause adverse effects reflect a failure to recognise the limitations of other sources of evidence about the effects of treatment.Large-scale randomized trial evidence shows that statin therapy reduces the risk of heart attacks, ischaemic strokes and coronary revascularization procedures ("major vascular events") by about one quarter for each mmol/L reduction in low density lipoprotein (LDL) cholesterol during each year (after the first) that it continues to be taken. The absolute benefits of statin therapy depend on an individual's absolute risk of occlusive vascular events and the absolute reduction in LDL cholesterol that is achieved. For example, lowering LDL cholesterol by 2 mmol/L (77 mg/dL) with an effective low-cost statin regimen (e.g. atorvastatin 40 mg daily, costing about £2 per

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“…Confounding is not a new phenomenon in the world of vitamin epidemiology. We and others have shown that social class and other lifestyle factors influence circulating levels of vitamins C and E and carotenoids, and as such confound associations of circulating vitamin levels with risk of chronic disease (37,38). Many similar confounding factors are potentially relevant in the field of vitamin D epidemiology, including studies on its relationship to inflammatory arthritis (Figure 1).…”

Section: Are Reverse Causality and Residual Confounding Potential Limmentioning

confidence: 97%

Is vitamin D in rheumatoid arthritis a magic bullet or a mirage? The need to improve the evidence base prior to calls for supplementation

Welsh

Peters

Sattar

2011

Arthritis & Rheumatism

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Those confounded vitamins: what can we learn from the differences between observational versus randomised trial evidence?

Cited by 404 publications

References 20 publications

Lung function and blood levels of copper, selenium, vitamin C and vitamin E in the general population

Lung function and blood levels of copper, selenium, vitamin C and vitamin E in the general population

Interpretation of the evidence for the efficacy and safety of statin therapy

Is vitamin D in rheumatoid arthritis a magic bullet or a mirage? The need to improve the evidence base prior to calls for supplementation

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