Various vitamin and mineral supplements are observed to increase mortality risk in older women, with the exception of calcium, which decreases risk
- Correspondence to Neva L Crogan
Department of Nursing, Gonzaga University, E. 503 Boone Ave., Spokane, WA 99258, USA;
Implications for practice and research
■ Antioxidant use could be harmful to older women.
■ Calcium use is associated with lower mortality risk in older women.
■ Dietary supplements should be used to treat symptomatic nutrient deficiency disease.
■ Further research is needed to explore the relationship between dietary supplement use and mortality risks.
Within the context of the Iowa Women's Health Study, Mursu et al assessed the relationship between dietary supplement use and total mortality risk among a large, population-based sample of older women. Previously, antioxidant use was thought to be protective. However, findings from this study provide evidence that some antioxidants may be harmful to older women.
The Iowa Women's Health Study,1 a population-based observational study, was designed to examine the relationships between dietary supplementation, lifestyle and the incidence of cancer in postmenopausal women. From the original 42 836 women aged 55–69 years recruited in 1986, a total of 38 772 completed a food frequency and supplement use questionnaire at baseline. Of those, 29 230 women answered the same supplement use questions in 1997, and 19 124 women again answered the supplement use questions in 2004. The supplements queried included multivitamins, vitamins A, β-carotene, B6, folic acid, B complex, C, D, E, iron, calcium, copper, magnesium, selenium and zinc. Collected demographic data included age, height, weight, education, place of residence (farm, rural area other than a farm or city), history of diabetes mellitus and/or high blood pressure, history of hormone replacement therapy, physical activity level and smoking history.
Descriptive, bivariate and multivariate data analyses were conducted using SAS statistical software. Bivariate analyses included analysis of variance for continuous variables and x2 tests for categorical variables. To determine absolute risk (increase and reduction), the absolute risk in the supplement groups was multiplied by the multivariable adjusted HR change in the non-supplement use group. The relationship between supplement use and outcomes were analysed using a Cox proportional hazards regression analyses. The researchers chose to compare three possible models: a minimally adjusted model, and two multivariable adjusted models.
Mursu et al found that the use of multivitamins, vitamin B6, iron, magnesium, zinc and copper were associated with increased mortality risk in older women. This association was strongest with supplemental iron. However, a review of the literature found little confirmatory evidence in regards to possible harmful effects of supplemental iron. Calcium use was found to be associated with decreased risk.
Previously, antioxidant use was thought to be protective. However, findings from this study are contrary to previous studies found in the literature and add to the growing evidence that certain antioxidants could be harmful to older women.2 3 However, the literature is not conclusive. Loria et al4 found that low serum vitamin C concentrations in men with cancer may have an increased risk of mortality, but not so in women.
Findings from this study should be considered and evaluated cautiously. As the study was observational, the researchers relied solely upon self-reported data from older women. Strengths of the study included a large sample size, the longitudinal design and the experience of the research team.
In conclusion, dietary supplement use should be individualised to the patient or client.Even though dietary supplements are easily obtained and purchased, specific dietary supplements (ie, calcium or iron) should be used only if recommended by a provider to treat identified or potential nutritional deficiencies and/or conditions.