Journal Watch General Medicine oppsummerer flere studier og en metaanalyse om vitamintilskudd: In 2006, sales of nutritional supplements exceeded $4.5 billion in the U.S. alone. This year, in several studies, researchers assessed whether supplements — especially with vitamins that are touted as antioxidants — are beneficial. … In total, these studies failed to show evidence […]
Journal Watch General Medicine oppsummerer flere studier og en metaanalyse om vitamintilskudd:
In 2006, sales of nutritional supplements exceeded $4.5 billion in the U.S. alone. This year, in several studies, researchers assessed whether supplements — especially with vitamins that are touted as antioxidants — are beneficial. … In total, these studies failed to show evidence of health benefit associated with vitamin supplementation across a broad set of clinical endpoints, and potential harm cannot be excluded. Patients should be told that little evidence supports the use of supplements other than for several specific indications (e.g., folic acid for pregnancy). The best advice is to return to mother’s directive — eat your fruits and vegetables.
Spis heller sunt, med andre ord: det er som kjent mer enn en type pillepushere. Og én kategori er et par hakk mindre regulert enn den som vanligvis får mest kjeft.
Det er forøvrig ingen ringere enn Aud Dalsegg i Dagbladet som bringer denne nyheten. Hun kan med andre ord være kritisk til alternativbransjen også, når hun bare vil.
Skjønt hun måtte jo la en av de alternative få siste (uimotsagte) ord:
Vitamin C motvirker infeksjoner og kan helbrede virusinfeksjon hvis dosen som gis er høy nok. En rekke forsøk som ikke har vist noen effekter har brukt doser på noen hundre milligram. Ofte trengs det imidlertid langt høyere doser, sier han.
Poleszynski peker også på at syntetiske vitaminer, som gjerne brukes i slike forsøk, ikke har samme virkning i kroppen som naturlige vitaminer.
Tja.
Det er liksom ikke mine felt noe av det, men det går jo an å gjøre et lite søk for å teste sin egen innbitte skepsis. Helt fra Poleszinsky dukket opp i min ungdom som overivrig leserbrevskribent for homøopati og annet jeg næret liten tillit til, har jeg nok hatt fordommer. Og at han er redaktør for det lett konspirasjonsfikserte* Mat og Helse gjør lite for å minske dem. Men dette er jo faktisk hans felt (selv om doktorgraden hans er i sosiologi).
Det siste, forskjellen på «syntetisk» og «naturlig» aner jeg virkelig ikke hva Poleszinsky eller journalisten har ment med, men betakaroten som kosttilskudd har unektelig hatt atskillig styggere resultat enn i gulrotform. Kanskje det er noe sånt som er ment?
Men til vitamin C, megadoser og derfra til den nysgjerriges gode venn Cochrane collaboration. Der dukker det opp en laaang rekke resultat på vitamin C, men bare få på vitamin C og infeksjon.
Her er dagens «top abstract» om vitamin c og forkjølelse:
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.
En mulig effekt under spesielle forhold, ellers ikke mye å skryte av.
Men dette kvalifiserer kanskje ikke som «megadoser» i Poleszinskys vokabular. Og Google Scholar forteller at et tidligere studium i (av alle tenkelige steder) Journal of Manipulative Physiological Therapy har forsøkt virkelige megadoser med god effekt:
METHOD: Investigators tracked the number of reports of cold and flu symptoms among the 1991 test population of the facility compared with the reports of like symptoms among the 1990 control population. Those in the control population reporting symptoms were treated with pain relievers and decongestants, whereas those in the test population reporting symptoms were treated with hourly doses of 1000 mg of Vitamin C for the first 6 hours and then 3 times daily thereafter. Those not reporting symptoms in the test group were also administered 1000-mg doses 3 times daily. RESULTS: Overall, reported flu and cold symptoms in the test group decreased 85% compared with the control group after the administration of megadose Vitamin C. CONCLUSION: Vitamin C in megadoses administered before or after the appearance of cold and flu symptoms relieved and prevented the symptoms in the test population compared with the control group.
Det høres da lovende ut, hva?
Nå er kanskje ikke det som virker å være et kiropraktororgan beste stedet å publisere slike resultat, så det kan muligens tas med en klype salt. Og et annet studie med megadoser ser litt annerledes ut:
Participants were randomised to receive one of four interventions: vitamin C in a daily dose of 0.03 g, 1 g or 3 g, or «Bio-C» (containing vitamin C [3 g daily] plus bioflavenoids [75 mg], rutin [150 mg], hisperidin [150 mg], rose hip extract [750 mg] and acerola [150 mg]). They were to take the medication at onset of cold symptoms and on the following two days.
Resultatet diskuteres med svakheter i studiet, mens funnet er relativt enkelt:
Our study found no significant differences in severity or duration of cold symptoms between groups who took low-dose (placebo) and high-dose vitamin C as treatment for the common cold. The lack of benefit from high-dose therapeutic vitamin C is consistent with the findings of four other randomised controlled trials2-5 (Box 1). … It is time to question again the wisdom and utility of the wide practice of well nourished adults taking mega-doses of vitamin C to treat the common cold, a practice which has become prevalent worldwide since the advocacy of Linus Pauling in the early 1970s.
Ironisk nok ble følgende også observert: «symptoms tended to be less severe and of shorter duration in the placebo group.»
Uansett var det visst ikke så lett å finne noen konsensus om at megadoser vitamin C hjelper mot forkjølelse.
Men det var bare forkjølelse. Cochrane Library har også en interessant oversikt over studier i forbindelse med lungebetennelse, hvilket ikke er noen liten infeksjon: «In the USA, pneumonia is the sixth most common cause of death and the most common cause of infection-related mortality».
Og ikke minst er det slik at
Certain populations have a high risk of pneumonia. In developing countries the incidence of lower respiratory tract infection in children has, at the upper extreme, been over 1000 cases per 1000 person-years (Selwyn 1990). Also, in many developing countries prevalence of malnutrition is high, indicating low vitamin C intakes. Another population group with an elevated risk of pneumonia is elderly people, since the incidence increases with age (Baik 2000; Hemilä 2004). A further population group with high risk of pneumonia is military recruits; the average incidence of pneumonia in marine and naval recruits in the 1970s was 60 per 1000 person-years in a US study (Pazzaglia 1983).
Her virker også resultatet langt mer positivt for vitamintilhengerne, dog innenfor noe annet enn megadosens rammer:
The prophylactic use of vitamin C to prevent pneumonia should be further investigated in populations who have high incidence of pneumonia, especially if dietary vitamin C intake is low. Similarly, the therapeutic effects of vitamin C should be studied especially in patients with low plasma vitamin C levels. The current evidence is too weak to advocate widespread prophylactic use of vitamin C to prevent pneumonia in the general population. However, therapeutic vitamin C supplementation may be reasonable for pneumonia patients who have low vitamin C plasma levels because its cost and risks are low.
Megadose-teorien får ingen imponerende støtte:
Subgroup analysis by vitamin C dosage less or more than 100 mg/day did not reveal any effect of the dose; however, the trials were clinically so heterogeneous and the number of cases so low so that we could not make any conclusions about dose-dependency.
Med unntak av et havsider om alt mulig rart via Google, var det i grunnen det vesentligste jeg fant på mitt korte raid, annet enn at en «masse» studier tydeligvis er igangsatt for å teste om intravenøst vitamin C i store doser har effekt på diverse kreftformer. (Fantastisk hvis det virker – å ta det gjennom munnen virket nemlig ikke.)
Sannsynligvis har god informasjon druknet i dette havet, men så langt fant jeg ikke all verden som tilsier at det er gode grunner til å handle megadoser av hverken det ene eller andre.
Andre finner (eller vet) kanskje mer?