If scientists were reincarnated as hunting dogs, many would be used in humorous skits because the rest of us can easily see and hear where the birds are hiding, but the scientists-turned-dogs would invariably be barking up the wrong tree.
Consider this piece of cluelessness about an important vitamin but an obviously wrong thesis:
Association of vitamin C with the risk of age-related cataract: a meta-analysis.
- 1Department of Ophthalmology, The Second Artillery General Hospital, Beijing, China.
Whether vitamin C is a protective factor for age-related cataract remains unclear. Thus, we conducted a meta-analysis to summarize the evidence from epidemiological studies of vitamin C and the risk of age-related cataract.
Pertinent studies were identified by searching in PubMed and in Webscience. The random effect model was used to combine the results. Meta-regression and subgroups analyses were used to explore potential sources of between-study heterogeneity. Publication bias was estimated using Egger’s regression asymmetry test.
Finally, 15 articles with 20 studies for vitamin C intake and eight articles with 10 studies for serum ascorbate were included in this meta-analysis. The relative risk (RR) and 95% confidence interval of cataract for the highest versus the lowest category of vitamin C intake was 0.814 (0.707-0.938), and the associations were significant in America and Asia. Significant association of cataract risk with highest versus the lowest category of serum ascorbate was found in general [0.704 (0.564-0.879)]. Inverse associations were also found between serum ascorbate and nuclear cataract and posterior subcapsular cataract.
Higher vitamin C intake and serum ascorbate might be inversely associated with risk of cataract. Vitamin C intake should be advocated for the primary prevention of cataract.
© 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.
age-related cataract; meta-analysis; serum ascorbate; vitamin C
- PMID: 25735187
- DOI: 10.1111/aos.12688
How did I know a priori that the thesis is ridiculous? An entire civilization that must have had marginal vitamin C intake was without any significant evidence for excess cataracts.
In the long cold winters, the isolated Swiss had a diet consisting of: 2-3 servings of meat per week (none or negligible vitamin C), raw milk (some vitamin C), raw dairy products derived from milk (mostly cheese and butter, even less due to processing out the vitamin C in the liquid phase), and rye bread (no vitamin C). If these people had glassy eyes like so many peoples do around the world, would Weston Price have failed to notice the problem and report it? No.
Since vitamin C consumption is obviously not a factor in cataract development, does the following study surprise us?
Antioxidant vitamin supplementation for preventing and slowing the progression of age-related cataract.
- 1MetroWest Medical Center, Framingham, Massachusetts, USA. email@example.com.
Age-related cataract is a major cause of visual impairment in the elderly. Oxidative stress has been implicated in its formation and progression. Antioxidant vitamin supplementation has been investigated in this context.
To assess the effectiveness of antioxidant vitamin supplementation in preventing and slowing the progression of age-related cataract.
We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2012, Issue 2), MEDLINE (January 1950 to March 2012), EMBASE (January 1980 to March 2012), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to March 2012), Open Grey (System for Information on Grey Literature in Europe) (www.opengrey.eu/), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). There were no date or language restrictions in the electronic searches for trials. The electronic databases were last searched on 2 March 2012. We also checked the reference lists of included studies and ongoing trials and contacted investigators to identify eligible randomized trials.
We included only randomized controlled trials in which supplementation with one or more antioxidant vitamins (beta-carotene, vitamin C and vitamin E) in any form, dosage or combination for at least one year was compared to another antioxidant vitamin or to placebo.
DATA COLLECTION AND ANALYSIS:
Two authors extracted data and assessed trial quality independently. We pooled results for the primary outcomes, i.e., incidence of cataract and incidence of cataract extraction. We did not pool results of the secondary outcomes – progression of cataract and loss of visual acuity, because of differences in definitions of outcomes and data presentation. We pooled results by type of cataract when data were available. We did not perform a sensitivity analysis.
Nine trials involving 117,272 individuals of age 35 years or older are included in this review. The trials were conducted in Australia, Finland, India, Italy, the United Kingdom and the United States, with duration of follow-up ranging from 2.1 to 12 years. The doses of antioxidant vitamins were higher than the recommended daily allowance. There was no evidence of effect of antioxidant vitamin supplementation in reducing the risk of cataract, cataract extraction, progression of cataract or in slowing the loss of visual acuity. In the pooled analyses, there was no evidence of effect of beta-carotene supplementation in reducing the risk of cataract (two trials) (relative risk (RR) 0.99, 95% confidence interval (CI) 0.91 to 1.08; n = 57,703) or in reducing the risk of cataract extraction (three trials) (RR 1.00, 95% CI 0.91 to 1.10; n = 86,836) or of vitamin E supplementation in reducing the risk of cataract (three trials) (RR 0.97, 95% CI 0.91 to 1.04; n = 50,059) or of cataract extraction (five trials) (RR 0.98, 95% CI 0.91 to 1.05; n = 83,956). The proportion of participants developing hypercarotenodermia (yellowing of skin) while on beta-carotene ranged from 7.4% to 15.8%.
There is no evidence from RCTs that supplementation with antioxidant vitamins (beta-carotene, vitamin C or vitamin E) prevents or slows the progression of age-related cataract. We do not recommend any further studies to examine the role of antioxidant vitamins beta-carotene, vitamin C and vitamin E in preventing or slowing the progression of age-related cataract. Costs and adverse effects should be weighed carefully with unproven benefits before recommending their intake above recommended daily allowances.
- [PubMed – indexed for MEDLINE]
Anyone knowing Weston Price’s observational data would not even have done this meta-analysis. A complete waste of time – killer counterexamples are real and smart scientists save time by paying attention to them.