Effect of Daily Vitamin E and Multivitamin-Mineral Supplementation on Acute Respiratory Tract Infections in Elderly Persons:  A Randomized Controlled Trial FREE

An age-related decline in immune response may increase the risk of infectious diseases and their complications.¹ Beneficial effects of micronutrient supplementation on immune response have been observed not only in institutionalized older persons but also in healthy noninstitutionalized elderly individuals.² Supplementation with multivitamins and minerals at the recommended dietary allowance (RDA) level mainly improved cellular immune parameters.^2- 3 For vitamin E, a higher dose, such as 200 mg/d, has been required to demonstrate an effect.⁴

For infectious disease occurrence, however, evidence demonstrating the efficacy of multivitamin-mineral supplementation at the RDA level^3,5 or at a high level⁴ is limited and studies have shown contradictory results. More specifically, the effect of multivitamin-mineral supplementation at physiological doses or of 200 mg of vitamin E on respiratory tract infections has not been investigated in noninstitutionalized elderly persons. Results in institutionalized elderly individuals have been inconsistent.^6- 8

The aim of our randomized intervention trial was to determine whether long-term daily supplementation with multivitamins and minerals at the RDA level or with 200 mg of vitamin E reduced incidence and severity of acute respiratory tract infections in noninstitutionalized elderly persons.

A total of 652 men and women (≥60 years) were enrolled in the randomized, double-blind, placebo-controlled trial. All together 11 417 individuals were invited to participate through 2 community-based sampling strategies: via the population registry of the town of Doetinchem, the Netherlands, and via direct mail to senior citizens' apartments in several other towns. Figure 1 shows the flow diagram of participants. Individuals were excluded if they used immunosuppressive treatment, anticoagulants interfering with vitamin K metabolism,⁹ or dietary supplements in the previous 2 months or if they had a history of cancer, liver disease, or fat malabsorption during the 5 years before randomization. Participants were enrolled between September 1, 1998, and March 23, 1999, and were followed up for a maximum of 15 months. Eleven participants in the multivitamin-mineral, 10 in the vitamin E, 11 in the multivitamin-mineral plus vitamin E, and 6 in the placebo groups did not meet the compliance criteria of taking at least 80% of their capsules but were included in both analyses; 26, 28, 26, and 25, respectively, were excluded from the per-protocol analysis for discontinuing the intervention. None of the reasons for discontinuing intervention were considered a result of the treatment.

Written informed consent was obtained prior to study participation. The medical ethics committee of Wageningen University, the Netherlands, approved the research protocol.

The following treatments were applied in a 2 × 2 factorial design: multivitamins and minerals, vitamin E, multivitamins and minerals plus vitamin E, and placebo. The multivitamin-mineral capsule contained: retinol (600 µg), beta-carotene (1.2 mg), ascorbic acid (60 mg), vitamin E (10 mg), cholecalciferol (5 µg), vitamin K (30 µg), thiamin mononitrate (1.4 mg), riboflavin (1.6 mg), niacin (18 mg), pantothenic acid (6 mg), pyridoxine (2.0 mg), biotin (150 µg), folic acid (200 µg), cyanocobalamin (1 µg), zinc (10 mg), selenium (25 µg), iron (4.0 mg), magnesium (30 mg), copper (1.0 mg), iodine (100 µg), calcium (74 mg), phosphor (49 mg), manganese (1.0 mg), chromium (25 µg), molybdenum (25 µg), and silicium (2 µg). We chose dosages at RDA levels for vitamins and 25% to 50% of RDA levels for minerals because multivitamin-mineral supplementation near RDA levels previously was shown to decrease duration of infections in noninstitutionalized elderly persons.³ The vitamin E capsule contained 200 mg/dL of α-tocopheryl acetate because this dose was suggested to be optimal for improving immune response.⁴ Placebo capsules contained soybean oil. Quality control of the capsules after treatment showed no decrease in the original contents.

Each participant received 2 capsules per day to be ingested with dinner for a maximum of 15 months. A computer-generated, 4-per-block, randomization list was created by the pharmacy (Roche Vitamins, Europe, Basel, Switzerland), allocating treatment to participant number. Block-randomization was used to obtain balanced groups over seasons. Numbered boxes containing identical-looking capsules were transported from the pharmacy to the Wageningen University. At enrollment, boxes were assigned consecutively to participants. Treatment allocation was kept at the pharmacy exclusively in sealed opaque envelopes while participant identity was known exclusively at the Wageningen University. None of the treatment codes was broken during the study period. After the investigator performed all analyses, the pharmacy disclosed the treatment list to the Wageningen University. Roche Vitamins, provided the randomization code and the supplements and performed the vitamin concentration analyses in this trial. The company was not involved in the design and conduct of the study, the collection, analyses, and interpretation of the data, or the preparation, review, approval, or control of the manuscript.

Participants completed a questionnaire about relevant population characteristics and supplement use at baseline, and yearly influenza vaccination after treatment. Body mass index was calculated by dividing weight in kilograms by the square of height in meters. Baseline plasma samples were collected for determination of α-tocopherol, ascorbic acid, retinol, and carotenoids. To monitor compliance, these assessments were repeated in a postintervention sample of a subset (n = 300). Returned capsules were counted for all participants.

The before and after intervention blood samples were collected between 8:30 and 11 AM. A light breakfast, without fruit or fruit juices, was allowed before sampling. Plasma was stored at − 80°C within 6 hours of blood draw. The reversed-phase high-pressure liquid chromatography method¹⁰ was used to analyze fat-soluble vitamin concentrations.¹¹ Ascorbic acid concentration was obtained via standard procedures and assessed by fluorometric assay.¹² Total cholesterol levels were analyzed using the enzymatic Chod-Pap method with Cobas-Bio centrifugal analyzer.¹³ Detection levels and intraday and interday repeatability were within normal ranges and were sufficient for all analyses.^10- 11 Suboptimal plasma vitamin levels were based on other studies in elderly persons.^14- 15

Main outcomes were incidence and severity of acute respiratory tract infections assessed using a diary in which participants, who received thorough instruction, recorded all acute symptoms. Acute symptoms were defined as follows (1) sudden onset, (2) a pattern that differed from any usual symptoms, and (3) 1 or more of the respiratory tract symptoms like rhinitis, sore throat, or cough persisted for at least 2 days.¹⁶ Presence of accompanying signs was also recorded in the diary: fever, phlegm production, wheezing, pain during breathing, headache, shivering, perspiration, muscular pain, malaise, tearful eyes, pain in facial sinuses, ear pain, staying in bed, restriction of daily activities, staying at home, and use of medication or other treatment. Indicators of severity were defined beforehand as (1) total duration of respiratory episodes, (2) number of symptoms, (3) percentage of participants with fever, (4) restriction of activity, or (5) episode-related medication.

Participants were requested to report symptoms of a possible acute respiratory tract infection by telephone to the study nurse who checked whether the symptoms met the definition. Rectal temperature was self-assessed with a study-supplied thermometer on all symptomatic days.

As a more specific diagnostic test, microbiology by polymerase chain reaction and serology tests were performed in a random subsample of 97 symptomatic patients during 107 illness episodes from October 1, 1998, until October 1, 1999. A nose-throat swab and acute-phase blood sample was taken within 3 days and a convalescent blood sample between 2 and 4 weeks after onset of symptoms. The nose-throat swab and paired blood sample were tested for the 9 most common respiratory pathogens: rhinovirus, enterovirus, coronavirus, respiratory syncytial virus, influenza virus A and B, parainfluenza virus, adenovirus, and Mycoplasma pneumoniae.^17- 19

Assuming an infection rate of 0.9 episodes per person per year and a 25% reduction in incidence, sample size calculations showed that with a power of 80% and an α of .05 (1 sided), 220 participants in the vitamin E and 220 individuals in the multivitamin and mineral group should be included. Power was regarded sufficient by including more than 300 participants in both groups, and infection rate was 1.59 per person per year. Although the initial sample size was based on a 1-sided test on the assumption that effects would only be seen in 1 direction, after the study was completed the need for 2-sided tests became evident. P values are therefore based on 2-sided tests.

An asymptomatic period of at least 7 days was required before a subsequent episode was recognized as a new infection. Participants were considered at risk of a new infection during the entire follow-up minus the duration of each illness episode, and minus 7 days following each episode. Data analysis was performed according to intention-to-treat (ie, based on all participants as randomized). A per-protocol analysis was also performed but did not substantively change the study results.

First, data were analyzed by 4 treatment groups separately. Second, after evaluating possible interactions, data were analyzed according to the 2 × 2 factorial design.

Continuous data are expressed as mean (SD) and compared using analysis of variance (ANOVA). Total carotenoid concentrations, total illness-duration, and the number of symptoms were log-transformed to account for nonnormality before ANOVA was performed and P values were obtained from ANOVA with log-transformed values. Frequencies, including percentages, were calculated for categorical data and these variables were compared by χ² tests. We used a Poisson regression model with number of episodes as the dependent variable, treatment group as the independent variable, and log-person time as the offset included in the model. P values less than .05 were regarded as statistically significant. Analyses were preformed using SAS statistical software version 6.12 (SAS Institute Inc, Cary, NC).

Baseline characteristics and plasma antioxidant-vitamin concentrations of the 652 participants were similar across groups (Table 1). Only 2% of the participants lived in homes for the aged. We therefore consider our study population to be noninstitutionalized. In total, 105 (16%) of 652 participants discontinued the intervention (Figure 1).

At baseline 40 (6%) and 1 (0.2%) of 652 individuals had suboptimal ascorbic acid and α-tocopherol concentrations, respectively. After intervention, ascorbic acid was suboptimal in 4 (1.3%) of 300 participants.

After treatment, ascorbic acid, total carotenoids, α-tocopherol, and cholesterol-adjusted α-tocopherol levels increased significantly in the multivitamin-mineral and multivitamin-mineral plus vitamin E group, while γ-tocopherol decreased significantly. In the vitamin E group, α-tocopherol and cholesterol-adjusted α-tocopherol levels increased significantly, while γ-tocopherol levels decreased significantly. In the placebo group, none of the measured vitamins changed significantly.

The median follow-up duration was 441 days in each group, representing complete follow-up for 15 months in 84% and including at least 3 winter months (October-February) for 92% of the participants. Of the 652 participants, 443 (68%) recorded a total of 1024 acute respiratory tract infection episodes. The study nurse received by telephone 763 (74.4%) of 1024 reports from 381 (86.0%) of 443 participants. Nearly all (99.2%; 757/763) reports were evaluated as acute respiratory tract infection, the symptoms being distinguishable from allergies. Infection was microbiologically confirmed in 62 (58%) of 107 of the symptomatic periods. In only 4 (4%) of 91 matched asymptomatic participants was a pathogen identified. The relatively high percentage of microbiological substantiation during the symptomatic periods supports the quality of the self-reported infections.^20- 21 A mean of 1.59 episodes was recorded per person per year. The multivitamin-mineral group had 240 episodes with 71% of the participants experiencing at least 1 episode, the vitamin E group had 280 episodes among 68%, the multivitamin-mineral plus vitamin E group had 274 episodes among 66%; and the placebo group had 230 episodes among 67%.

To assess treatment effect, we first analyzed incidence and severity of the 4 treatment groups separately (Table 2). The only significant difference among the treatment groups was the percentage of participants who experienced restriction of activity, which was significantly lower in the multivitamin-mineral group compared with placebo.

Second, the 2 × 2 factorial design was used to obtain a more stable estimate of incidence and severity. Neither incidence nor severity was significantly different between the multivitamin-mineral and the no multivitamin-mineral groups (Table 3). Incidence was not significantly different between the vitamin E and the no-vitamin E groups. However, severity tended to be greater in the vitamin E group. Among participants receiving vitamin E and experiencing an infection, total illness-duration and total number of symptoms were significantly higher, and fever and restriction of activity occurred more frequently, than those in the no-vitamin E groups (Table 4). Furthermore, when 1-sided tests were used as originally planned, no P values were significant for any of the tests except for the effect of vitamin E on illness severity.

For all microorganisms demonstrated, frequency was not different among the 4 treatment groups (Table 5). After study completion, participants completed a questionnaire asking what they thought the supplemental vitamins contained. Of the 652 participants, 437 (67%) had no idea what the capsule contained, 169 (26%) had the wrong idea, and 46 (7%) were correct.

This randomized placebo-controlled trial demonstrates that long-term daily supplementation with a physiological dose of multivitamins and minerals or with 200 mg of vitamin E did not lower incidence and severity of acute respiratory tract infections in noninstitutionalized elderly persons. However, among persons experiencing an infection, those individuals who received vitamin E instead had longer total illness duration, more symptoms, and a higher frequency of fever and restriction of activity.

In our trial, 94% of the participants met the compliance criteria of 80% capsule intake. Accordingly, the multivitamin-mineral and vitamin E group showed a large increase in plasma vitamin concentrations, whereas this was not the case in the placebo group. Baseline characteristics were well balanced across groups. Assessment of infectious disease was based on self-report, which may have led to misclassification. However, such misclassification would have been nondifferential (ie, similar for all groups), resulting in possible underestimation of the treatment effect. We tried to assess the outcome as accurately as possible: a prospective diary, telephone calls, home visits, measuring rectal temperature, plus microbiological and serological testing in a sample. This method of assessing infection has been used before and follows widely accepted criteria.^3- 4,7- 8 An infection was confirmed in 58% of the symptomatic periods. This percentage is high compared with other studies in which a general practitioner or study nurse evaluated symptoms.^20- 21 Therefore, the outcome assessment in our study seems to have been reasonably accurate. Finally, one may argue that an asymptomatic period of 7 days is inadequate to discriminate between exacerbation of previous infections and new episodes. Although arbitrarily chosen, this period is considerably longer than asymptomatic periods of previous studies.^22- 23

Past studies of multivitamin and mineral supplementation in noninstitutionalized elderly persons addressed incidence and duration of infectious diseases in general.^3,5 Supplementation trials that specifically focused on incidence of acute respiratory tract infections have been performed only in institutionalized elderly patients.⁸ In the latter intervention studies, incidence was not reduced, consistent with our findings. On the contrary, Chandra³ reported a decreased duration of infectious diseases in noninstitutionalized elderly individuals. However, in that study the proportion of individuals with suboptimal blood vitamin concentrations was much higher. Since Girodon et al⁸ did not observe a lower incidence in institutionalized elderly individuals, it may not be surprising that multivitamin and mineral supplementation in our population did not decrease incidence of acute respiratory tract infections. The low percentage of participants having suboptimal micronutrient status may reflect a relatively well nourished population and may explain the lack of a treatment effect. The rationale for the selection of noninstitutionalized elderly persons was based on an improved immune response after multivitamin and mineral supplementation in such populations³ although this may not necessarily translate to a hard end point such as respiratory tract infections. It is conceivable that particular subgroups of elderly persons who have suboptimal micronutrient concentrations might benefit from additional dietary supplementation.

The only previous studies of vitamin E supplementation in noninstitutionalized elderly persons were intended to measure immune response and assessed infectious diseases only as a secondary outcome. A lower incidence of all infections was reported in noninstitutionalized elderly individuals⁴ while Harman et al⁶ observed no effect on incidence of respiratory tract infections in institutionalized elderly patients. Although not statistically significant, a higher incidence of upper respiratory tract infection in those supplemented with 50 or 100 mg of vitamin E was observed by Pallast et al.²⁴ We could find no published data on vitamin E supplementation and the severity of respiratory tract infections.

Many investigators have reported that supplementation with vitamin E improves immune response by enhancing lymphocyte proliferation and IL-2 production and by decreasing prostaglandin E₂ (PGE₂) production by affecting cyclooxygenase 2 activity.^4,9 Others have shown no positive relation between vitamin E and immune indices.^25- 26 It should be realized that our observed effect of vitamin E on severity of illness might even reflect a more effective immune response.

Vitamin E may improve immunity by being converted into an α-tocopheroxyl radical. This radical can act as a prooxidant unless it is reduced by ascorbic acid or glutathione.^27- 28 The prooxidant mechanism of vitamin E has not yet been thoroughly assessed.²⁸ Possibly, a balance between antioxidants is important in the prooxidant role of vitamin E. An imbalance may be more pronounced after long-term supplementation with one nutrient administered in amounts much higher than the RDA level. Azzi and Stocker²⁷ suggest that the antioxidant effect of vitamin E is not the primary action of this vitamin. Recently, inhibitory effects of vitamin E on protein kinase C and glutathione S-transferase π have been reported.^27,29

Most previous studies suggest a beneficial effect of multivitamin, mineral, and vitamin E supplementation on immune response. From a public health point of view, studying incidence of infections, especially the frequent respiratory tract infections, has much greater relevance. Studies have reported that 50% of elderly people use dietary supplements,³⁰ with multivitamin, mineral, and vitamin E supplements being the most common.^30- 31 It would be worthwhile to study the effect of multivitamins and minerals in elderly people with suboptimal plasma concentration of vitamins. If our results are confirmed and vitamin E exacerbates respiratory tract infections, elderly people, especially those who are already well-nourished, should be cautious about taking vitamin E supplements.