4 replies to this topic

[doug123]

A Cochrane Review was published recently:

This version first published online: October 18. 2004
Date of last subtantive update: May 14. 2007

...on the effectiveness of at least 0.2 grams/day (200mg/day -- US RDA is 60 mg/day) Vitamin C. BBC News ran a mainstream report on the matter, and it's called: Vitamin C 'does not stop colds' . I tried to take a slightly closer look at the Cochrane Review myself -- as Cochrane Reviews are generally taken seriously by the medical community.

For my felllow laymen, I'd like to provide some introductory background information on Cochrane Review. If you're totally unfamiliar with Cochrane Review, I might suggest clicking here to review: "The Cochrane Group's handbook for systematic reviewers of interventions."

Here's some information regarding Cochrane's systematic review from Wikipedia (I think that this information was accurate as of June 25, 2007):

Systematic review

From Wikipedia, the free encyclopedia

Jump to: navigation, search

A Systematic review is a literature review focused on a single question which tries to identify, appraise, select and synthesis all high quality research evidence relevant to that question. Systematic reviews are generally regarded as the highest level of medical evidence by evidence-based medicine professionals. An understanding of systematic reviews and how to implement them in practice is becoming mandatory for all professionals involved in the delivery of health care.

A systematic review is a summary of healthcare research that uses explicit methods to perform a thorough literature search and critical appraisal of individual studies to identify the valid and applicable evidence. It often, but not always, uses appropriate techniques (meta-analysis) to combine these valid studies

While many systematic reviews are based on an explicit quantitative meta-analysis of available data, there are also qualitative reviews which nonetheless adhere to the standards for gathering, analyzing and reporting evidence.

Many healthcare journals now publish systematic reviews, but the best-known source is the Cochrane Collaboration, a group of over 6,000 specialists in health care who systematically review randomised trials of the effects of treatments and, when appropriate, the results of other research. Cochrane reviews are published in the Cochrane Database of Systematic Reviews section of the Cochrane Library, which to date (February 2007) contains 2,893 complete reviews and 1,646 protocols.

The Cochrane Group provides a handbook for systematic reviewers of interventions, where they suggest that each systematic review should contain the following main sections:

o Background
o Objectives
o Methods of the review
o Results
o Conclusion and discussion

There are seven steps for preparing and maintaining a systematic review, as outlined in the Cochrane Handbook:

1.  Formulating a problem
2.  Locating and selecting studies
3.  Critical appraisal of studies
4.  Collecting data
5.  Analyzing and presenting results
6.  Interpreting results
7.  Improving and updating reviews

First, here's the Cochrane review summary on this matter -- i.e. this is sort of layman's terms:

Vitamin C for preventing and treating the common cold

This is a Cochrane review abstract and plain language summary, prepared and maintained by The Cochrane Collaboration, currently published in The Cochrane Database of Systematic Reviews 2007 Issue 3, Copyright © 2007 The Cochrane Collaboration. Published by John Wiley and Sons, Ltd.. The full text of the review is available in The Cochrane Library (ISSN 1464-780X).
This record should be cited as: Douglas RM, Hemilä H, Chalker E, Treacy B. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD000980. DOI: 10.1002/14651858.CD000980.pub3
This version first published online: October 18. 2004
Date of last subtantive update: May 14. 2007

Douglas RM, Hemilä H, Chalker E, Treacy B

Summary

The term 'the common cold' does not denote a precisely defined disease, yet the characteristics of this illness are familiar to most people. It is a major cause of visits to a doctor in Western countries and of absenteeism from work and school. It is usually caused by respiratory viruses for which antibiotics are useless. Other potential treatment options are of substantial public health interest.

Since vitamin C was isolated in the 1930s it has been proposed for respiratory infections, and became particularly popular in the 1970s for the common cold when (Nobel Prize winner) Linus Pauling drew conclusions from earlier placebo-controlled trials of large dose vitamin C on the incidence of colds. New trials were undertaken.

This review is restricted to placebo-controlled trials testing at least 0.2 g per day of vitamin C. Thirty trials involving 11,350 participants suggest that regular ingestion of vitamin C has no effect on common cold incidence in the ordinary population. It reduced the duration and severity of common cold symptoms slightly, although the magnitude of the effect was so small its clinical usefulness is doubtful. Nevertheless, in six trials with participants exposed to short periods of extreme physical or cold stress or both (including marathon runners and skiers) vitamin C reduced the common cold risk by half.

Trials of high doses of vitamin C administered therapeutically (starting after the onset of symptoms), showed no consistent effect on either duration or severity of symptoms. However, there were only a few therapeutic trials and their quality was variable. One large trial reported equivocal benefit from an 8 g therapeutic dose at the onset of symptoms, and two trials using five-day supplementation reported benefit. More therapeutic trials are necessary to settle the question, especially in children who have not entered these trials.

So here's the Cochrane review abstract itself on Vitamin C for preventing and treating the common cold:

Abstract

Background
The role of vitamin C (ascorbic acid) in the prevention and treatment of the common cold has been a subject of controversy for 60 years, but is widely sold and used as both a preventive and therapeutic agent.

Objectives
To discover whether oral doses of 0.2 g or more daily of vitamin C reduces the incidence, duration or severity of the common cold when used either as continuous prophylaxis or after the onset of symptoms.

Search strategy
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 4, 2006); MEDLINE (1966 to December 2006); and EMBASE (1990 to December 2006).

Selection criteria
Papers were excluded if a dose less than 0.2 g per day of vitamin C was used, or if there was no placebo comparison.

Data collection and analysis
Two review authors independently extracted data and assessed trial quality. 'Incidence' of colds during prophylaxis was assessed as the proportion of participants experiencing one or more colds during the study period. 'Duration' was the mean days of illness of cold episodes.

Main results
Thirty trial comparisons involving 11,350 study participants contributed to the meta-analysis on the relative risk (RR) of developing a cold whilst taking prophylactic vitamin C. The pooled RR was 0.96 (95% confidence intervals (CI) 0.92 to 1.00). A subgroup of six trials involving a total of 642 marathon runners, skiers, and soldiers on sub-arctic exercises reported a pooled RR of 0.50 (95% CI 0.38 to 0.66).

Thirty comparisons involving 9676 respiratory episodes contributed to a meta-analysis on common cold duration during prophylaxis. A consistent benefit was observed, representing a reduction in cold duration of 8% (95% CI 3% to 13%) for adults and 13.6% (95% CI 5% to 22%) for children.

Seven trial comparisons involving 3294 respiratory episodes contributed to the meta-analysis of cold duration during therapy with vitamin C initiated after the onset of symptoms. No significant differences from placebo were seen. Four trial comparisons involving 2753 respiratory episodes contributed to the meta-analysis of cold severity during therapy and no significant differences from placebo were seen.

Authors' conclusions
The failure of vitamin C supplementation to reduce the incidence of colds in the normal population indicates that routine mega-dose prophylaxis is not rationally justified for community use. But evidence suggests that it could be justified in people exposed to brief periods of severe physical exercise or cold environments.

Personally, when I saw the BBC news headline: "Vitamin C 'does not stop colds,'" I didn't assume that's all the info to be learned from this review. I will re-copy what else can be learned besides what seems to be pretty inconclusive evidence to suggest that Vitamin C is effective to reduce incidence of common cold:

Authors' conclusions

The failure of vitamin C supplementation to reduce the incidence of colds in the normal population indicates that routine mega-dose prophylaxis is not rationally justified for community use. But evidence suggests that it could be justified in people exposed to brief periods of severe physical exercise or cold environments.

So I'm not going to stop taking vitamin C. I'll definitely keep trying to remind myself to take some Vitamin C before I work out or enter a cold environment!

Also, you may note from the summary:

Nevertheless, in six trials with participants exposed to short periods of extreme physical or cold stress or both (including marathon runners and skiers) vitamin C reduced the common cold risk by half

Also, you may note that the studies included in this meta analysis were at least 0.2g/day, and 500mg Vitamin C is in fact ~833% of US RDA. So more or less than 0.2 grams (200mg) a day -- or over 3 times more that US RDA might yield different results. Someone please correct me (or my math) if I made a mistake. Edit: math error fixed.

This may indicate that these six studies were flawed (or that the others without parallel results may be), used a different dose, maybe different forms of Vitamin C -- further examination of these six studies may be warranted; however, I see no evidence to suggest taking 0.2 grams/day (200mg/day) of Vitamin C may be unsafe. Does anyone else?

Thoughts or comments?

Take care.

Edited by adam_kamil, 19 July 2007 - 12:31 AM.

[krillin]

http://books.nap.edu...069351&page=125

In a case-control comparison of 77 subjects with cataract and 35 control subjects with clear lenses, vitamin C intakes of greater than 490 mg/day were associated with a 75 percent decreased risk of cataracts compared with intakes of less than 125 mg/day (Jacques and Chylack, 1991). Similarly, vitamin C intakes greater than 300 mg/day were associated with a 70 percent reduced risk of cataracts (Robertson et al., 1989). In a second case-control comparison with 1,380 cataract patients and 435 control subjects, similar results were found: although intake numbers were not reported, above-median vitamin C intake was associated with a 20 percent decrease in the risks of cataracts (Leske et al., 1991). In contrast, an analysis of data derived from the Baltimore Longitudinal Study on Aging found no increased association between 260 mg/day of vitamin C and risk of cataracts compared to 115 mg/day (Vitale et al., 1993).

In an 8-year prospective study, Hankinson et al. (1992) evaluated the experience of more than 50,000 nurses in the Nurses Health Study. Dietary vitamin C intakes were not associated with a decreased risk of cataract, but cataract risk was 45 percent lower among the nurses who consumed vitamin C supplements for 10 or more years. With a cohort of 247 nurses from the above study, vitamin C supplement use, in amounts ranging from less than 400 mg/day to greater than 700 mg/day for 10 years or more, was associated with a statistically significant protective effect on lens opacities (Jacques et al., 1997). Women who consumed vitamin C supplements for less than 10 years were not protected.

[mike250]

more vitamin C

Biol Psychiatry. 2002 Aug 15;52(4):371-4.

High-dose ascorbic acid increases intercourse frequency and improves mood: a randomized controlled clinical trial.

Brody S.

Center for and the Psychosomatic and Psychobiological Research, University of Trier, Germany.

BACKGROUND: Ascorbic acid (AA) modulates catecholaminergic activity, decreases stress reactivity, approach anxiety and prolactin release, improves vascular function, and increases oxytocin release. These processes are relevant to sexual behavior and mood. METHODS: In this randomized double-blind, placebo-controlled 14 day trial of sustained-release AA (42 healthy young adults; 3000 mg/day Cetebe) and placebo (39 healthy young adults), subjects with partners recorded penile-vaginal intercourse (FSI), noncoital partner sex, and masturbation in daily diaries, and also completed the Beck Depression Inventory before and after the trial. RESULTS: The AA group reported greater FSI (but, as hypothesized, not other sexual behavior) frequency, an effect most prominent in subjects not cohabiting with their sexual partner, and in women. The AA but not placebo group also experienced a decrease in Beck Depression scores. CONCLUSIONS: AA appears to increase FSI, and the differential benefit to noncohabitants suggests that a central activation or disinhibition, rather than peripheral mechanism may be responsible.



Psychopharmacology (Berl). 2002 Jan;159(3):319-24. Epub 2001 Nov 20.

A randomized controlled trial of high dose ascorbic acid for reduction of blood pressure, cortisol, and subjective responses to psychological stress.

Brody S, Preut R, Schommer K, Schurmeyer TH.

Center for psychomatic and Psychobiological Research, University of Trier, Trier, Germany. stuartbrody@hotmail.com

RATIONALE: Physiological responses to stress are considered disruptive to health. High-dose ascorbic acid has reduced indices of stress in laboratory animals. METHODS: We conducted a randomized double-blind, placebo-controlled 14-day trial of sustained-release ascorbic acid (60 healthy young adults; 3 x1000 mg/day Cetebe) and placebo (60 healthy young adults) for reduction of blood pressure, cortisol, and subjective response to acute psychological stress (Trier Social Stress Test, TSST, consisting of public speaking and mental arithmetic). Six subjects from each group were excluded. RESULTS: Compared to the placebo group, the ascorbic acid group had less systolic blood pressure (an increase of 23 versus 31 mmHg), diastolic blood pressure, and subjective stress responses to the TSST; and also had faster salivary cortisol recovery (but not smaller overall cortisol response). Cortisol response to 1 microg ACTH, and reported side-effects during the trial did not differ between groups. Plasma ascorbic acid level at the end of the trial but not pre-trial was associated with reduced stress reactivity of systolic blood pressure, diastolic blood pressure, and subjective stress, and with greater salivary cortisol recovery. CONCLUSIONS: Treatment with high-dose sustained-release ascorbic acid palliates blood pressure, cortisol, and subjective response to acute psychological stress. These effects are not attributable to modification of adrenal responsiveness.

[inawe]

If we put all the above together what conclusion can we arrive at?
Qoute: ascorbic acid increases intercourse frequency
Quote: marathon

Does that mean that if we take vitamin C we will be impelled into "marathon intercourse frequency"? OH NO!!!

[wiserd]

I'm not sure that the cold is ascorbate's best target. People tend to forget ascorbate's role in collagen formation and focus on its antioxidant activity. Many diseases ( herpes family viruses are just one example ) tend to deliberately interfere with collagen formation as a way of promoting their spread.

Also, ascorbate aids in the production of glutathione. So in addition to colds and marathons, it should also help with chemical stressors. Alcohol usage is one example (though ascorbate exacerbates certain types of chemical stressors like some forms of chromium)

Also, sugar in the blood or intestines discourages ascorbate absorption, and so diabetics tend to have pathologically low levels of plasma ascorbate. Thus the slow wound healing of diabetics, since collagen can't be produced fast enough. Most animals can produce ascorbate from sugar, but the last gene in the chain is nonsense for humans. If someone could find a way to restore that gene or the enzyme it produces, it would probably be very helpful for both type 1 and type 2 diabetes.

Diabetics can benefit from mixed ascorbates administered after exercise when blood sugar is lower.

Mixed ascorbates, like potassium ascorbate, magnesium ascorbate, calcium ascorbate etc. are better than ascorbic acid. When I megadosed on ascorbic acid I got small mouth ulcers. I switched to ascorbate salts and the problem went away. Sodium ascorbate, while standard for I.V. administered ascorbate, has the same problems that too much sodium has. Be careful of Trader Joe's mixed ascorbates, as they contain way more chromium than is good for your health.

Megadosing here means titrating to bowel tolerance. In other words, you take as much ascorbate over the course of the day as your body can absorb, with another dose every three or four hours. It's been helpful for me in temporarily relieving symptoms, but if you get just a bit too much you wind up with severe gas or diarrhea. Whether there's any problem taking more than a gram of ascorbate a day is debatable. A gram of ascorbate a day would actually make a good USRDA. Above that, needs vary widely based on health (if you're sick or stressed you need a lot more) and side effects are debated.

Ascorbate has the real interesting effect of decreasing tolerance to opiates, so they can be used longer without becoming addictive. The mechanism by which opiate tolerance develops is different than the mechanism by which opiate agonists work. Theoretically, heroine and morphine type drugs don't need to be addictive.

One thing to consider; since ascorbate helps your body clear a lot of different chemicals from your system you should be careful of taking it before an operation since you can clear the anesthetic from your system before the operation is over. Same with any other medication whose dosage is carefully controlled.

Edited by wiserd, 12 August 2007 - 11:00 PM.