Begrenzte Evidenz für einen günstigen Effekt von Vitamin-C-Supplementierung auf Biomarker von Herz-Kreislauf-Erkrankungen: Umbrella-Review

Der Umbrella-Review fand bei kardiovaskulären Biomarkern begrenzte, inkonsistente Evidenz und keinen einheitlichen Nutzen der Vitamin-C-Supplementierung.

Welche Evidenz zusammengeführt wurde

Ein Umbrella-Review fasst nicht unmittelbar einzelne Versuchspersonen zusammen, sondern wertet bereits vorhandene systematische Reviews und Metaanalysen aus. Hier suchten zwei Reviewer in vier Datenbanken nach Arbeiten zur Vitamin-C-Supplementierung und zu Biomarkern von Herz-Kreislauf-Erkrankungen. Die Suche reichte bis Februar 2018.

Eingeschlossen wurden 10 systematische Reviews beziehungsweise Metaanalysen mit zusammen 6.409 Teilnehmenden. Die jeweiligen Kontrollbedingungen stammten aus den eingeschlossenen Reviews. Bewertet wurden sowohl die Stärke der Evidenz als auch die methodische Qualität.

Welche Endpunkte betrachtet wurden

Die Synthese umfasste arterielle Steifigkeit, Blutdruck, Endothelfunktion, Blutzucker- und Insulinwerte sowie das Lipidprofil. Diese Messgrößen sind Biomarker oder Surrogatendpunkte. Sie können Hinweise auf physiologische Veränderungen geben, sind aber nicht mit einem nachgewiesenen Rückgang von Herzinfarkten, Schlaganfällen oder Sterbefällen gleichzusetzen.

Die im Quellenbereich aufgeführten Arbeiten bilden die paketgebundene Review-Familie: den Umbrella-Review, die darin gebundenen Reviews beziehungsweise Metaanalysen und deren zugeordnete Evidenzeinheiten. Für die einzelnen Konstituenten werden hier keine eigenständigen Ergebnisbehauptungen abgeleitet.

Was der Gesamtbefund zeigt

Über die eingeschlossenen Reviews hinweg ergaben sich keine Gesamteffekte auf arterielle Steifigkeit, Insulin, Gesamtcholesterin oder HDL-Cholesterin. Einzelne Reviews berichteten dagegen Verbesserungen bei Blutdruck, Glukose, LDL-Cholesterin und Triglyzeriden.

Diese Kombination aus Nullbefunden und einzelnen positiven Signalen begründet die zurückhaltende Schlussfolgerung des Umbrella-Reviews. Sie zeigt kein konsistentes Muster, das einen allgemeinen günstigen Effekt der Vitamin-C-Supplementierung auf das gesamte kardiovaskuläre Biomarkerprofil belegen würde.

Wie belastbar das Ergebnis ist

Bei der Endothelfunktion war die Heterogenität hoch. Das bedeutet, dass sich die zusammengeführten Studien beziehungsweise Reviews in ihren Ergebnissen oder Bedingungen deutlich unterschieden. Zusätzlich stufte die Arbeit die methodische Evidenzbasis als schwach ein.

Die betrachteten Endpunkte, Populationen, Mengen und Kontrollbedingungen waren nicht einheitlich. Positive Subgruppensignale dürfen deshalb weder kausal überhöht noch als gesicherter klinischer Nutzen ausgegeben werden. Auch aus Veränderungen von Biomarkern lässt sich allein keine Aussage zur Vermeidung klinischer Herz-Kreislauf-Ereignisse ableiten.

Fazit

Der Umbrella-Review über 10 Reviews und 6.409 Teilnehmende fand begrenzte, inkonsistente Evidenz: Einige Biomarker veränderten sich in einzelnen Synthesen günstig, während für mehrere andere kein Gesamteffekt bestand. Hohe Heterogenität und methodische Schwächen begrenzen die Aussagekraft zusätzlich.

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