Post by Matti NarkiaOn Fri, 12 Jan 2007 01:34:16 GMT,
Post by Heikki HeinonenPost by Mika MelaEi pidä paikkaansa. Asiaa on tutkittu jo kauan ja viime vuosina lääkärit
ja farmaseutitkin ovat alkaneet omakohtaisten kokemusten perusteella
tunnustaa että kyllähän se tuntuu auttavan. Itse olen vuosien ajan
syönyt 3-6g/vrk C-vitamiinia flunssaoireiden ilmaannuttua ja suositellut
samaa ystävillenikin. Innoittajana toimi Impakti 4/99:ssä ollut
artikkeli "C-vitamiini ja flunssa - pitkän kiistelyn kohde". Tokihan
jengi tuohon aikaan, kuten lekuritkin joille asiasta mainitsi, suhtautui
hieman huvittuneesti asiaan mutta ne jotka kokeilivat, sanoivat
järjestään kaikki tyyliin "no en tiedä oliko se se C-vitamiini vai ei
mutta kyllähän tuo flunssa helpottui ja meni nopeasti ohi". No, nyt kun
asiasta googlasin niin näköjään tämäkin asia on vihdoin tunnustettu
koululääketieteen parissa.
Omakohtaiset kokemuksesi lienevät placeboa. Myös mainitsemasi lääkärit ja
farmaseutit ovat ihan yhtä alttiita placeboefektille. Yhtä hyvin voisitte syödä
vaikka jäniksen papanoita. Kaikki perustuu vain uskoon. Eikä mitään ole
"tunnustettu koululääketieteen parissa". Tuo on tyypillistä huuhaata.
Olet väärässä. Vaikutukset ovat melko vähäisiä, muta niitä on todettu.
Luepa
Douglas RM, Hemila H.
Vitamin C for preventing and treating the common cold.
PLoS Med. 2005 Jun;2(6):e168; quiz e217. Epub 2005 Jun 28.
PMID: 15971944 [PubMed - in process]
<http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0020168>
<http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15971944>
Douglas RM, Hemila H, D'Souza R, Chalker EB, Treacy B.
Vitamin C for preventing and treating the common cold.
Cochrane Database Syst Rev. 2004 Oct 18;(4):CD000980. Review.
PMID: 15495002 [PubMed - indexed for MEDLINE]
<http://www.mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD000980/frame.html>
<http://medicine.plosjournals.org/archive/1549-1676/2/6/supinfo/10.1371_journal.pmed.0020168.sd001.pdf>
Oheisena PDF-tiedostosta kappaleet DISCUSSION ja REVIEWERS'
CONCLUSIONS sekä yksi COMMENTS AND CRITICISMS-kappaleista:
"DISCUSSION
The term 'the common cold' does not denote a precisely defined
disease, yet the characteristics of this illness are familiar
to most lay-people. Medically, it is a complex condition caused
by a broad range of viruses that are transmitted in varying
ways. There is no unanimously accepted definition for the
condition that can be used for the practical definition of
outcome in community based controlled trials. Instead, various
authors have used different operational definitions such as a
minimum set of symptoms. This variation in outcome definition
could be contributing to heterogeneity in results, but we have
not been able to explore this possibility.
Although the importance of the placebo-effect has been
challenged (Hrobartsson 2001) we considered that with the
expected small effects of vitamin C, and the greatly subjective
outcome definitions, only placebo-controlled trials could yield
information of adequate rigour to meet our study objectives.
Most of the trials analysed in this review were reported to be
double-blind, but that was not used as a selection criterion.
Also we did not restrict the review to trials using random
allocation and there are some trials included which had
alternative allocation. Sensitivity analysis indicated that a
restriction to trials for which requirements of allocation
concealment were known to be met, did not alter the principal
conclusions from our overview.
Despite the variation in methodology and the substantial
heterogeneity in results from this large number of trial
results carried out over a sixty year period, a rather coherent
story has emerged from the review.
Effect on common cold incidence
Consistent with earlier reviews (Hemilä 1997c, First Edition of
Cochrane Review 1998) we found no convincing reduction in
common cold incidence in the prophylaxis trials when the
subgroup of marathon runners and skiers and soldiers on su-
arctic operations were excluded from the trial pool (RR = 0.98;
95% CI: 0.95 to 1.00). A previous meta-analysis identified
three trials with participants under severe acute physical
stress which had found significant benefit from vitamin C
supplementation (Hemilä 1996b), The more recent trials by
Peters 1996a, Moolla 1996a and Himmelstein 1998a have
reinforced and extended those observations. The small study
reported by Sabiston 1974 which involved troops engaged in
brief exercises in subarctic conditions, shares with this group
of trials a low relative risk and a benefit that borders on
significance. It is noteworthy that all of the studies in this
group, involved brief exposure to high physical and/or cold
stress and that they were not uniformly using high doses of
vitamin C. One of us (Hemilä 1997c) has also previously drawn
attention to the possibility that some of the earlier benefits
observed in low dose or controlled trials without a placebo,
which were ruled ineligible for this review (Baird 1979;
Glazebrook 1942), might be a consequence of suboptimal dietary
intakes in British males. This might also explain the
significant reported benefits in the Charleston 1972 study
though participants in that study were single-blind and not
randomized. Few of the recent trials have estimated the dietary
intakes of vitamin C, but we cannot ignore the fact that
vitamin C is an essential nutrient and all participants in the
trials had regular intakes of this substance at some level,
some of them with lower levels than others.
The large, well conducted trial by Anderson 1972 reported a
statistically significant but quite small reduction in common
cold incidence. This trial was conducted during winter in
Toronto, Canada, and participants were selected on the basis of
having had problems with colds during previous winters. The
relative risk observed in that trial was 0.91, the risk
difference was 0.07, and thereby the number needed to treat
(NNT) estimated from the study was 14. A cold Canadian winter
might be a part explanation for the benefit in this trial if it
is true that cold as well as physical stress makes a
prophylactic benefit for vitamin C more likely. Furthermore, as
regards the possible interaction between supplementation and
dietary vitamin C levels, this Anderson 1972 trial is
interesting as the investigators found 48% reduction by vitamin
C in "total days indoors" among participants who consumed <3 oz
of fruit juices, whereas vitamin C reduced total days indoors
by only 22% among those who consumed more juices. Similar
modifying effect by fruit juices was found in the therapeutic
trial by Anderson 1975.
Effect on common cold duration and severity: prophylaxis trials
Both in adults and in children, regular vitamin C
supplementation resulted in a statistically highly significant
reduction in the duration of respiratory episodes that occurred
during the prophylactic supplementation period. For children,
the pooled estimate was 13.6%, and for adults it was 8.0%.
Although these findings point to a definite physiological
effect by prophylactic vitamin C on common cold duration, the
practical significance of these findings is less convincing. It
would not seem reasonable to ingest vitamin C regularly in the
mega-dose range throughout the year if the only anticipated
benefit is to rather slightly shorten the duration of colds
which occur for adults, two or three times per year. Our pooled
estimate suggests that long term supplementation might result
in an upper estimate average reduction of annual common cold
morbidity from about 12 days (based on Douglas 1979;
unpublished Australian data) to about 11 days per year for
adults. For children under 12, who experience colds more
frequently (on average for this age, the upper estimate could
be as high as 28 days of cold morbidity annually, our pooled
estimate of benefit suggests that long term prophylaxis might
be associated with an average reduction in four symptom days
from about 28 days to 24 days per year per child. Such a
benefit is not trivial, but is it worth the cost of long term
prophylaxis, and could an equivalent benefit perhaps be
achieved in children through therapy alone?
In view of the consistent effect of vitamin C on the duration
of colds, an evident question is whether there might be dose
dependency, as suggested in a previous overview (Hemilä 1999a)
that might translate to a benefit when vitamin C is used
therapeutically. However, across the available pool of trials,
duration would appear to be more determined by the nature of
the participants than by dose. There are few trials that have
used more than 1 g/day in the child and adult groups
separately. Nevertheless, Karlowski 1975 and Coulehan 1974 used
two different doses within the same trials, i.e. with the same
outcome definitions. Karlowski's paper shows that for adults 6
g/day was associated with a double benefit compared with 3
g/day, and Coulehan 1974 found that for schoolchildren 2 g/day
caused about twice the benefit of 1 g/day (Hemilä 1996b; Hemilä
1999a). Although these findings do not establish dose
dependency, they support the case for examination of higher
doses.
Regular vitamin C prophylaxis also led to some decrease in
severity when measured as days indoors or days off work or
school, but the effect was not unambiguous on severity score
scales (Figure 3). These measures of severity are substantially
more heterogeneous than the measures of symptom duration and
the number of trials reporting data pertinent to 'severity' is
small.
On the issue of the severity of colds, the Pitt 1979 paper is
of further interest. This was a randomized placebo-controlled
double-blind trial with 674 marine recruits during an eight
week period using 2 g/day of vitamin C. There was no difference
in common cold incidence and only a 2% reduction in duration of
colds and 5% reduction in severity (p = 0.023). However, eight
of the recruits developed pneumonia as a sequel to their colds
and only one of these was in the vitamin C group (p = 0.077).
Thus, in addition to the common cold, vitamin C might also
affect other respiratory infections either independently of
colds, or as complications of colds (Hemilä 1999b).
Effect on common cold duration and severity: therapeutic trials
Because the prophylaxis trials have relatively consistently
shown that vitamin C affects duration and, to some extent, the
severity of the common cold, without changing their incidence
in the normal population, it might seem rational to administer
vitamin C therapeutically, starting immediately after the first
symptoms. But the therapeutic trials that have evaluated this
have been negative (Figures 4 and 5). The pooled estimates for
duration and severity do not find any difference between
vitamin C and placebo.
Technically the therapeutic trials are in some ways more
complicated than regular supplementation trials. If the timing
of initiation or the duration of supplementation affect the
benefit, false negative findings might result. Cowan 1950 used
a therapeutic dose of 6g in the first two days of illness with
no effect on duration. Elwood 1977, Tyrrell 1977, and Audera
2001 used a three day supplementation, and these three trials
found no effect by vitamin C. A five-day therapeutic trial by
Anderson (1975) found a reduction in 'days spent indoors per
subject' because of illness by 25% (p = 0.05) in the vitamin C
group (1-1.5 g/day). Also, using a five-day therapeutic
supplementation of 3 g/day in a 2x2 factorial design trial,
Karlowski (1975) reported that colds were 0.73 days shorter (p
= 0.10; see Hemilä 1996b). These tfindingsare consistent with
the possibility that three days might be too short a time for
vitamin C to produce unambiguous benefits, and it seems that
possible future therapeutic trials should use longer than three
day supplementation.
Also, the possibly larger effect observed by 8 g compared with
4 g as a single dose in the Anderson 1974 trial would seem to
suggest that future therapeutic trials with adults should use
doses larger than 4 g per day.
Furthermore, none of the therapeutic trials have examined the
effect of vitamin C on children, although the effect of
prophylaxis on duration has been substantially greater in
children compared with adults, and children have substantially
higher incidence of acute respiratory tract infections.
Experimental prophylaxis trials
The summary evidence from the three experimental studies, which
differed in their method of exposing volunteers to the
infecting virus is instructive. The studies by Dick and his
colleagues which have only been reported in conference
proceedings, paid careful attention to the severity of the
colds experienced by those who acquired them from fellow
volunteers who had been inoculated with a known rhinovirus.
They also found that in these more natural circumstances of
acquiring the virus, less, but not significantly less,
volunteers on vitamin C developed cold symptoms but
demonstrated similar viral shedding in the vitamin C group. The
tantalisingly fragmentary descriptions of the Dick studies show
clearly a biological effect of high dose vitamin C on the
nature and course of symptoms encountered. The findings appear
to confirm the view from the community prophylaxis studies that
the protective benefit from vitamin C comes into play after the
virus has become established.
Pauling's contribution
Among the four trials included in Pauling's (Pauling 1971a)
meta-analysis, the largest dose, 1 g/day, was used by Ritzel
(Ritzel 1961). Pauling based his optimistic quantitative
expectations on this rather small and brief trial. Ritzel found
significant reduction in the incidence (-45%) and duration
(-31%) of colds, and Pauling derived a combination of the
duration and incidence, which he labelled 'integrated
morbidity' referring to the total sickness days per person
during the trial.
This was reduced by 61% in the Ritzel trial. Pauling (Pauling
1971a) used these Ritzel findings to extrapolate the effects of
vitamin C to a broader community. The present analysis suggests
that 'integrated morbidity' is not a good outcome measure,
since the effects on incidence and duration/severity seem to
have quite different patterns though in the case of the Ritzel
study they moved together.
Further, Ritzel carried out his trial with schoolchildren in a
skiing school in the Swiss Alps, and such children are not a
representative selection of the general population, even though
technically the trial was randomized, double-blind and placebo-
controlled. In our analysis, Ritzel's trial is included in the
group of trials exposed to short lived severe acute physical
stress and/or cold environment which highlights the special
character of this trial.
Pauling's vigorous advocacy was undoubtedly the stimulus for a
wave of good trials, which now enable us to better understand
the rather confusing role that this substance plays in defence
against the common cold. Significant uncertainties still
persist, which further research could help to elucidate.
REVIEWERS' CONCLUSIONS
Implications for practice
The lack of effect of prophylactic vitamin C supplementation on
the incidence of common cold in normal populations throws doubt
on the utility of this wide practice. In special circumstances,
where people are engaged in extreme physical exertion and/or
exposed to significant cold stress the current evidence
indicates that vitamin C supplementation may have a
considerable beneficial effect, but caution should be exercised
in generalizing this finding that is mainly based on marathon
runners.
The prophylaxis trials found 8% reduction in common cold
duration in adults, and 13.6% reduction in children, but the
practical relevance of these findings are open, since the
therapeutic trials carried out so far have not found benefits
and this level of benefit probably does not justify long term
prophylaxis in its own right.
In summary, on the basis of our analysis, there seems no
justification for routine mega-dose vitamin C supplementation
in the normal population. Prophylaxis may be justified in those
exposed to severe physical exercise and/or cold. So far,
therapeutic supplementation has not been shown to be
beneficial.
Implications for research
With the findings from our analyses, it does not seem worth
while to carry out further regular prophylaxis trials in the
normal population. However there will be value in better
understanding the role of vitamin C in those exposed to heavy
exertion and cold stress. The findings in marathon runners,
skiers and soldiers operating in sub-arctic conditions warrant
further research.
None of the therapeutic trials carried out so far has examined
the effect of vitamin C on children, even though the
prophylaxis trials have found substantially greater effect on
duration in children. In view of the greater incidence of
respiratory infections in children such therapeutic trials are
warranted, especially where there is known to be sub-optimal
dietary intake of vitamin C.
The findings in the Anderson 1974 studies on the therapeutic
use of very high doses of 4 g and 8 g on the day of onset of
respiratory symptoms are tantalising and deserve further
assessment in the light of the uncertainties raised by the
problems with the placebo groups in that important study.
[...]
COMMENTS AND CRITICISMS
Doses too small
Summary:
One gram daily is a small dose. Most mammals make 3 or more
grams in their livers. Any practitioner of orthomolecular
medicine knows that a minimum of several grams a day is needed
to surely prevent a cold, and as much as 20 grams to cure one
in progress. Not one trial in your RCT's qualifies.
I certify that I have no affiliations with or involvement in any
organisation or entity with a direct financial interest in the
subject matter of my criticisms
Author's Reply:
The practitioners of orthomolecular medicine have not to our
knowledge published any controlled trial evidence on which this
comment is based. As we have said in the review, there is no
reasonable doubt that vitamin C supplementation plays some
biological role in defence, and there is tantalising evidence
from the Anderson 1974 study that a single therapeutic dose of
8 grams at commencement of a cold may have had a useful
therapeutic effect. We believe there is a case for rigorous
evaluation of the possibility that very large doses (of the
order of 8g daily in adults for periods up to five days after
the onset of symptoms) could produce benefits that were not
seen at lower doses.
In view of the greater propensity of children to colds and the
greater benefits observed in the child prophylaxis studies,
they may be the group in which to explore this approach (with
an appropriately pro-rated dose for weight). We add however a
caution. Although studies in which doses of 1 or 2 g daily of
vitamin C have been used for several months have not produced
convincing evidence of adverse effects to the volunteers.
Dosage of the kind discussed here needs to be carefully
monitored for adverse effects especially in children.
Contributors:
Reuven Gilmore"
Post by Matti Narkiasekä Harri Hemilän artikkeli "C-vitamiini ja flunssa - pitkän
kiistelyn kohde" Impaktin numeron 4/99
<http://finohta.stakes.fi/NR/rdonlyres/694B6317-DEB1-48B2-B224-D14F180D154B/0/Impakti1999_4.pdf>
sivulta 15.
Artikkeli löytyy myös HTML-muodossa sivulta
<http://www2.stakes.fi/finohta/impakti/1999/04/index-C-vitami.html>
Oheisena artikkelin koko teksti:
"C-vitamiini ja flunssa - pitkän kiistelyn kohde
Käsitys C-vitamiinin hyödyllisyydestä nuhakuumeen eli flunssan
ehkäisyssä ja hoidossa elää sitkeänä. Asia ei ole kokonaan
vailla tieteellistäkään näyttöä, mutta lopullinen vastaus
tuntuu edelleen jäävän ilmaan. Tutkimus jatkuu, sillä flunssan
kourissa vietettyjen sairaspäivien vähentämisellä olisi suuri
merkitys sekä potilaille itselleen että koko kansantaloudelle.
Nobelisti asialla
Ensimmäiset väitteet C-vitamiinin hyödystä flunssaa vastaan
julkaistiin 1930- luvulla. Laajaan julkisuuteen aihe tuli vasta
70- luvulla, kun kemian nobelisti Linus Pauling kirjoitti
kansantajuisen bestsellerin "Vitamin C and the Common Cold."
Siinä hän väitti C-vitamiinin estävän flunssia ja lievittävän
niiden oireita. Pauling laati myös meta-analyysin neljästä
lumekontrolloidusta tutkimuksesta ja päätteli, että flunssien
vähentyminen C-vitamiiniryhmissä tuskin johtui pelkästä
sattumasta. Paulingin kirjoitusten seurauksena aiheesta tehtiin
kymmeniä uusia kontrolloituja tutkimuksia. Niiden tulokset ovat
paljolti ristiriitaisia, mutta eräitä johtopäätöksiä voidaan
kuitenkin tehdä.
Riittääkö näyttö?
Taudin puhkeaminen
C-vitamiinin vaikutusta flunssan ilmaantuvuuteen on tutkittu
kuudessa suuressa tutkimuksessa, joissa oli yhteensä yli 3 500
koehenkilöä. Kun tutkimusten tulokset yhdistettiin, oli C-
vitamiiniryhmien (annos 1-3 g/pv) ja lumeryhmien välinen ero
flunssan ilmaantuvuudessa -1% (95% CI: -7%, +4%)1. Tämän
perusteella on selvää, etteivät C-vitamiinin lisäannokset estä
flunssia länsimaisessa keskivertoväestössä. Useissa pienemmissä
tutkimuksissa C-vitamiini kuitenkin on vähentänyt flunssien
ilmaantuvuutta. Mahdollisesti nämä tulokset heijastavat
todellisia vaikutuksia, joilla voi olla merkitystä rajatuissa
ihmisryhmissä.
Kolmessa lumekontrolloidussa tutkimuksessa selvitettiin C-
vitamiinin vaikutusta koehenkilöille, jotka olivat akuutin
fyysisen stressin alla. Yhdessä tutkimuksessa koehenkilöt
olivat koululaisia hiihtoleirillä, toisessa kanadalaisia
varusmiehiä talvisella harjoitusleirillä ja kolmannessa
maratonkilpailijoita Etelä-Afrikassa. C-vitamiini vähensi
näissä tutkimuksissa flunssien lukumäärää keskimäärin 50 % (95
% CI: -65%, -31%)2.
Neljässä brittimiehillä tehdyssä tutkimuksessa C-vitamiini
vähensi flunssien lukumäärää kontrolliryhmiin verrattuna 30 %
(95 % CI: -40%, -19%)1. Muihin Länsi-Euroopan maihin verrattuna
Isossa-Britanniassa C-vitamiinin saanti on ollut erityisen
alhaista, mikä voi selittää juuri briteillä havaitun hyödyn
lisäannoksista1.
Oireet ja kesto
C-vitamiini on johdonmukaisesti lievittänyt flunssan oireita ja
lyhentänyt kestoa, kun tarkastellaan lumekontrolloituja
tutkimuksia, joissa on käytetty suuria C-vitamiiniannoksia (³ 1
g/pv)3-8. Tulokset ovat kuitenkin vaihdelleet paljon. Viidessä
tutkimuksessa aikuiset saivat C-vitamiinia 1 g/pv ja flunssat
lyhentyivät keskimäärin 6 %. Kahdessa tutkimuksessa lapset
saivat C-vitamiinia 2 g/pv ja flunssat lyhentyivät 26 %8.
Keskimäärin isommat annokset ovat siis olleet hyödyllisempiä ja
keskimäärin lapset ovat hyötyneet enemmän. Selkein viite
annoksen merkityksestä saatiin Karlowskin ym. (1975)
tutkimuksessa, joka suoritettiin Yhdysvalloissa. 3 g/pv C-
vitamiinia lyhensi flunssien kestoa 6-9 %, mutta tupla-annos 6
g/pv lyhensi 17 % eli kaksinkertaisesti7,8.
Vaihtoehtolääkinnän piirissä esitetään usein suhteettomia
odotuksia C-vitamiinin hyödyllisyydestä, kun toiveita verrataan
tutkimustuloksiin. Lääketieteen piirissä ongelma on
päinvastainen, ja C-vitamiinin merkitystä vähätellään suuresti
tutkimustuloksiin verrattuna. Jälkimmäinen ongelma on
mielenkiintoisempi, koska lääketieteessä erityisesti
korostetaan tavoitetta, että toiminnan on perustuttava
tutkimuksiin.
Salapoliisityötä meta-analyysien parissa
Thomas Chalmersin vuonna 1975 laatimalla katsauksella C-
vitamiinin ja flunssan yhteydestä on pitkään ollut keskeinen
asema tässä keskustelussa. Siihen viitataan edelleen, kun
väitetään että C-vitamiini on täysin tehoton flunssiin.
Edesmennyt Chalmers oli kontrolloitujen tutkimusten uranuurtaja
ja meta-analyysin vaikutusvaltainen puolestapuhuja, mikä lisäsi
katsauksen painoarvoa. Chalmers laski julkaistuista tuloksista,
että keskimääräinen ero flunssan kestossa C-vitamiini- ja
lumeryhmien välillä oli -0,11 päivää (SE 0,24). Ero ei ole
merkitsevä kliinisesti eikä tilastollisesti. Allekirjoittanutta
vaivasi ristiriita Chalmersin meta-analyysin ja alkuperäisten
tutkimusten välillä. Huolellisessa vertailussa ilmeni, että
Chalmersin katsauksessa oli virheellisiä numeroarvoja ja
laskuvirheitä, ja että tutkimusten valintakin oli
virheellistä5. Jos halutaan testata Paulingin väitteitä gramma-
annosten hyödystä, täytyy rajautua tutkimuksiin, joissa on
käytetty suuria annoksia. Chalmers kuitenkin sisällytti meta-
analyysiinsä sellaisiakin tutkimuksia, joissa käytettiin C-
vitamiinia vain 0,025-0,2 g/pv. Kun jätin pois tällaiset
pienillä annoksilla tehdyt tutkimukset ja otin julkaisuista
oikeat numero-arvot, laskin samoista tutkimuksista C-vitamiini-
ja lumeryhmien eroksi -0,93 päivää (SE 0,22), mikä on kahdeksan
kertaa suurempi ero kuin Chalmersin laskema5. Meta-analyysi on
tärkeä menetelmä useiden alkuperäistutkimusten yhdistämisessä
ja se on tullut jäädäkseen. Chalmersin meta-analyysin ongelmat
kuitenkin havainnollistavat sitä, että erilaiset subjektiiviset
valinnat ja jopa selkeät virheet voivat vääristää meta-
analyysin johtopäätöksiä. Kirjallisuudessa on muitakin
esimerkkejä meta-analyyseistä, joiden johtopäätökset ovat
ristiriitaisia, vaikka kysymyksenasettelu on näennäisesti
sama9,10. Ei ole syytä olla liian hyväuskoinen meta-analyysien
tulosten suhteen, varsinkin jos aihe on itselle täysin vieras.
Koskien C-vitamiinia ja flunssaa, Chalmersin katsauksen lisäksi
eräät muutkin yhteenvedot ovat harhaanjohtavia ja
virheellisiä4,6.
Tutkimus jatkuu
Julkaistujen tutkimusten perusteella Pauling oli oikeassa siinä
suhteessa, että C-vitamiinilla on vaikutusta sekä flunssan
ilmaantuvuuteen että oireisiin, mutta hän oli aivan liian
optimistinen hyödyn suuruuden suhteen. Toisaalta, flunssa on
niin yleinen ongelma, että 20 %:n lyhentyminen kestossa tai
30-50 %:n estovaikutus pienissäkin ihmisryhmissä on
mielenkiintoinen kysymys, erityisesti kun C-vitamiini on
vaaraton ja halpa ravintoaine (70 penniä/gramma). C-vitamiinin
käytännön merkitys on avoin, mutta julkaistut tulokset antavat
selkeän motiivin jatkotutkimuksille.
Harri Hemilä
LL, FT, dosentti
Kansanterveystieteen laitos
Helsingin yliopisto
Lähteet
1 Hemilä H. Vitamin C intake and susceptibility to the common
cold. Br J Nutr 1997;77:59-72 ja 78:857-66
2 Hemilä H. Vitamin C and common cold incidence: a review of
studies with subjects under heavy physical stress. Int J Sports
Med 1996;17:379-83
3 Hemilä H. Auttaako C-vitamiini vilustumiseen? Duodecim
1990;106:1306-11
4 Hemilä H. Onko C-vitamiinitableteilla fysiologisia
vaikutuksia? Suom Lääkäril 1995;50:2360-2
5 Hemilä H, Herman ZS. Vitamin C and the common cold: a
retrospective analysis of Chalmers' review. J Am Coll Nutr
1995;14:116-23
6 Hemilä H. Vitamin C supplementation and common cold symptoms:
problems with inaccurate reviews. Nutrition 1996;12:804-9
7 Hemilä H. Vitamin C, the placebo effect, and the common cold.
A case study of how preconceptions influence the analysis of
results. J Clin Epidemiol 1996;49:1079-84 ja 1085-7
8 Hemilä H. Vitamin C supplementation and common cold symptoms:
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Matti Narkia