Water-soluble vitamins influence the development of an adequate structure of bone tissue, but there is scant information relating them with osteoporotic fractures. We analyze whether serum vitamin C, vitamin B12, and erythrocyte folate, or dietary intake of vitamin C and folate, are related with osteoporotic fractures in the elderly. A hospital-based case-control study was carried out at the Hospital of Jaén (167 cases, 167 controls), Spain. Cases were defined as patients aged 65 or more years with a low-energy fracture. Controls were people without fracture, matched for age and sex with cases. Diet was assessed by a semi-quantitative food frequency questionnaire. Serum vitamin C was measured using high-performance liquid chromatography (HPLC). Folic acid and vitamin B12 were measured using procedures of competitive or immunometric immunoassay. Multivariable analyses were also fitted to adjust for confounding using analysis of covariance (for the comparison of adjusted means) and conditional logistic regression (for estimating adjusted odds ratios). A statistically significant difference between cases and controls for vitamin C blood levels was found, being higher for controls (p = 0.01). Analysis of the association between serum vitamin C and fracture risk showed a linear trend (p = 0.03) with a significantly reduced risk for the upper quartile (OR = 0.31; 95% CI 0.11-0.87). The intake of vitamin C, folic acid, and B12 was not related to fracture risk, nor was there any association with erythrocyte folate or serum vitamin B12. In conclusion, serum vitamin C levels were lower in cases with osteoporotic fractures than in controls.

The present review aims to answer 3 questions: does publication bias need to be assessed in meta-analyses?; what procedures, not requiring complex statistical approaches, can be applied to detect it?; and should other factors be taken into account when interpreting the procedures? The first question is easy to answer. Publication bias is a potential threat to the validity of the conclusions of meta-analyses. Therefore, both the MOOSE and QUOROM statements include publication bias in their guidelines; nevertheless, many meta-analyses do not use these statements (e.g., meta-analyses conducted by the Cochrane Collaboration), perhaps because they use a comprehensive search strategy. There are many methods to assess publication bias. The most frequently used are funnel plots or <>, <> (which allow the effects of bias to be estimated), and methods based upon regression on plots, such as Egger's method and funnel plot regression. An advantage of these methods is that they can only be applied using published data. However, agreement between these methods in detecting bias is often poor. Therefore, application of more than one method to detect publication bias is recommended. To correctly interpret the results, the number of pooled studies should be more than 10 and the existence of heterogeneity in the pooled estimate must be taken into account.

INTRODUCCIÓNLos epidemiólogos, dentro de los salubristas, son los más inclinados a importar o crear nuevos métodos de investigación que intenten arrojar algo más de luz al estudio de los determinantes de la enfermedad. Uno de esos procedimientos traídos a la salud públi-ca por los epidemiólogos ha sido el metaaná-lisis. El metaanálisis no fue una técnica originada en el seno de la salud pública. El tér-mino fue acuñado por Glass en 1976, un psicólogo de la educación 1 .Desde esa fecha muchos han querido ver precedentes de este procedimiento en autores de prestigio. En diferentes artículos y libros se ha ido retrocediendo cada vez más en el tiempo. Primero fue un trabajo de MacMahon y Hutchison, en el que exponían una Rev Esp Salud Pública 2006; 80: 483-489 N. RESUMENEl metaanálisis tiene precedentes, incluso en Confucio (siglo VI AC) se puede apreciar una frase relativa a la síntesis del conocimiento. El metaanálisis es fruto del paradigma inductista de investigación que nos gobierna. Dentro de él nos ofrece un análisis del principio de consistencia para una asociación causal (2º principio de Hill). Ha motivado el desarrollo de cuestionarios y protocolos de evaluación de diferentes tipos de diseños, principalmente de ensayos clínicos. Todo esto fue uno de los detonantes de lo que se ha dado en llamar medicina basada en la «evidencia» (mejor «pruebas» en castellano). Ha impulsado la creación de agencias de evaluación de tecnologías sanitarias y favorecido el reconocimiento de los profesionales de salud pública más conocedores del método de investigación. Sus contribuciones a la salud pública no se pueden separar de las realizadas en otras especialidades, pero en el campo de la metodología de investigación ha contribuido de manera decisiva al estudio del sesgo de publicación y la búsqueda de variables que influyen en la heterogeneidad, la existencia de discrepancia entre los estudios individuales.Palabras clave: Metaanálisis. Revisiones sistemáticas. ABSTRACT Contributions of systematic review and meta-analysis to public healthMeta-analysis has several precedents; even in Confucius (VI BC) one can found a sentence about the synthesis of knowledge. Meta-analysis is a consequence of the paradigm of induction. Within this paradigm of research, meta-analysis gives an analysis of the principle of consistency of a causal association (2 nd principle of Hill). It has promoted the development of evaluation questionnaires and protocols for different designs, mainly clinical trials. It favoured the movement of evidence-based medicine, which is behind the creation of agencies for the evaluation of health technologies, and the recognition of public health professionals dedicated to research methods (mainly epidemiologists). The contributions of meta-analysis to public health are not distinguishable from others made to other specialties, although in the field of research methods it has contributed to the study of publication bias and to the search of determinants of heterogeneity, the lack of consistency among the individual...