Lowered risks of hypertension and cerebrovascular disease after vitamin/mineral supplementation: the Linxian Nutrition Intervention Trial

Homocysteine lowering interventions for preventing cardiovascular events

BACKGROUND

Cardiovascular disease such as coronary artery disease, stroke and congestive heart failure, is a leading cause of death worldwide. A postulated risk factor is elevated circulating total homocysteine (tHcy) levels which is influenced mainly by blood levels of cyanocobalamin (vitamin B12), folic acid (vitamin B9) and pyridoxine (vitamin B6). There is uncertainty regarding the strength of association between tHcy and the risk of cardiovascular disease.

OBJECTIVES

To assess the clinical effectiveness of homocysteine-lowering interventions (HLI) in people with or without pre-existing cardiovascular disease.

SEARCH STRATEGY

We searched The Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (issue 3 2008), MEDLINE (1950 to August 2008), EMBASE (1988 to August 2008), and LILACS (1982 to September 2, 2008). We also searched in Allied and Complementary Medicine (AMED; 1985 to August 2008), ISI Web of Science (1993 to August 2008), and the Cochrane Stroke Group Specialised Register (April 2007). We hand searched pertinent journals and the reference lists of included papers. We also contacted researchers in the field. There was no language restriction in the search.

SELECTION CRITERIA

We included randomised clinical trials (RCTs) assessing the effects of HLI for preventing cardiovascular events with a follow-up period of 1 year or longer. We considered myocardial infarction and stroke as the primary outcomes. We excluded studies in patients with end-stage renal disease.

DATA COLLECTION AND ANALYSIS

We independently performed study selection, risk of bias assessment and data extraction. We estimated relative risks (RR) for dichotomous outcomes. We measured statistical heterogeneity using I(2). We used a random-effects model to synthesise the findings.

MAIN RESULTS

We included eight RCTs involving 24,210 participants with a low risk of bias in general terms. HLI did not reduce the risk of non-fatal or fatal myocardial infarction, stroke, or death by any cause (pooled RR 1.03, 95% CI 0.94 to 1.13, I(2) = 0%; pooled RR 0.89, 95% CI 0.73 to 1.08, I(2) = 15%); and pooled RR 1.00 (95% CI 0.92 to 1.09, I(2): 0%), respectively.

AUTHORS' CONCLUSIONS

Results from available published trials suggest that there is no evidence to support the use of HLI to prevent cardiovascular events.

Dietary supplement use and mortality in a cohort of Swedish men

The use of dietary supplements has increased substantially in most industrialized countries. The aim of this study was to prospectively examine the association between use of dietary supplements and all-cause mortality, cancer mortality and CVD mortality in men. We used the population-based prospective cohort of 38 994 men from central Sweden, 45–79 years of age, with no cancer or CVD at baseline and who completed a self-administered FFQ including questions on dietary supplement use and life-style factors in 1997. During average 7.7 years of follow-up, 3403 deaths were ascertained; among them, 771 due to cancer and 930 due to CVD (during 5.9 years of follow-up). In multivariate adjusted models including all men there was no association observed between use of any dietary supplement or of multivitamins, vitamin C, vitamin E or fish oil specifically and all-cause mortality, cancer or CVD mortality. Among current smokers, regular use of any supplement was associated with statistically significant increased risk of cancer mortality: relative risk (RR) 1·46 (95 % CI 1·06, 1·99). Among men reporting an inadequate diet at baseline (assessed by Recommended Food Score), there was a statistically significant inverse association between use of any dietary supplement and CVD mortality (RR 0·72; 95 % CI 0·57, 0·91), no associations were observed among men with adequate diets. In conclusion, we cannot exclude that the use of dietary supplements is harmful for smokers. On the other hand, among men with an insufficient diet, the use of supplements might be beneficial in reducing CVD mortality.

The 677 C/T MTHFR polymorphism is associated with essential hypertension, coronary artery disease, and higher homocysteine levels

BACKGROUND

Essential hypertension (EH) and cardiovascular disease are common, multifactorial disorders likely to be influenced by multiple genes of modest effect. The C677T methylenetetrahydrofolate reductase (MTHFR) gene polymorphism is related to MTHFR enzyme activity and to plasma homocysteine (Hcy) concentration. This study was designed to investigate an association of this polymorphism with coronary artery disease (CAD), EH, and healthy subjects.

METHODS

In this study, we measured serum folate, serum vitamin B12, and plasma homocysteine and determined the MTHFR C677T genotype of 78 patients with essential hypertension, 100 patients with coronary artery disease, and 100 healthy subjects. MTHFR genotypes were assessed by real-time polymerase chain reaction.

RESULTS

CC, CT, and TT genotype frequencies were 52, 44.0, and 4.0% in patients with CAD, respectively. In patients with essential hypertension, the CC, CT, and TT genotype frequencies were 46.2, 41.0, and 12.8%, respectively. In control subjects, the CC, CT, and TT genotype frequencies were 72.0, 26.0, and 2.0%, respectively. The C allele was significantly more frequent in controls compared with patients with EH (p<0.05), and CC genotypes were more frequent in controls compared to patients with EH and CAD. Homocysteine level was higher in TT genotypes in CAD patients compared with CC and CT genotypes (p<0.01). MTHFR gene polymorphism is an independent risk factor for EH but not for CAD.

CONCLUSIONS

The TT genotype of the 677C/T MTHFR polymorphism is associated with EH and CAD. In addition, TT genotypes had higher plasma Hcy levels in CAD patients compared with CC and CT genotypes. MTHFR gene polymorphism is an independent risk factor for EH but not for CAD.

A prospective study of polymorphisms of DNA repair genes XRCC1, XPD23 and APE/ref-1 and risk of stroke in Linxian, China

BACKGROUND

Stroke is the leading cause of death in Linxian, China. Although there is evidence of DNA damage in experimental stroke, no data exist on DNA repair and stroke in human populations.

AIM

To assess the risk of stroke conferred by polymorphisms in the DNA repair genes, XRCC1, XPD23 and APE/ref-1 in a cohort of individuals originally assembled as subjects in two cancer prevention trials in Linxian, China.

METHODS

The subjects for this prospective study were sampled from a cohort of 4,005 eligible subjects who were alive and cancer free in 1991 and had blood samples available for DNA extraction. Using real-time Taqman analyses, all incident cases of stroke (n = 118) that developed from May 1996, and an age- and a sex-stratified random sample (n = 454) drawn from all eligible subjects were genotyped. Cox proportional hazards models were used to estimate relative risks (RRs) and 95% CIs.

RESULTS

No association was observed between polymorphisms in APE/ref-1 codon 148 and XRCC16 codon 194, and stroke. Polymorphisms in XRCC110 codon 399 were associated with a significantly reduced risk of stroke (RR 0.59, 95% CI 0.36 to 0.96, p = 0.033), whereas XPD23 codon 312 was associated with a significantly increased risk of stroke (RR 2.18, 95% CI 1.14 to 4.17, p = 0.010).

CONCLUSIONS

Polymorphisms in DNA repair genes may be important in the aetiology of stroke. These data should stimulate research on DNA damage and repair in stroke.

Efficacy of folic acid supplementation in stroke prevention: a meta-analysis

BACKGROUND

The efficacy of treatments that lower homocysteine concentrations in reducing the risk of cardiovascular disease remains controversial. Our aim was to do a meta-analysis of relevant randomised trials to assess the efficacy of folic acid supplementation in the prevention of stroke.

METHODS

We collected data from eight randomised trials of folic acid that had stroke reported as one of the endpoints. Relative risk (RR) was used as a measure of the effect of folic acid supplementation on the risk of stroke with a random effect model. The analysis was further stratified by factors that could affect the treatment effects.

FINDINGS

Folic acid supplementation significantly reduced the risk of stroke by 18% (RR 0.82, 95% CI 0.68-1.00; p=0.045). In the stratified analyses, a greater beneficial effect was seen in those trials with a treatment duration of more than 36 months (0.71, 0.57-0.87; p=0.001), a decrease in the concentration of homocysteine of more than 20% (0.77, 0.63-0.94; p=0.012), no fortification or partly fortified grain (0.75, 0.62-0.91; p=0.003), and no history of stroke (0.75, 0.62-0.90; p=0.002). In the corresponding comparison groups, the estimated RRs were attenuated and insignificant.

INTERPRETATION

Our findings indicate that folic acid supplementation can effectively reduce the risk of stroke in primary prevention.

Homocysteine, traditional risk factors and impaired renal function in coronary artery disease

BACKGROUND

To establish whether the frequent finding of a moderate-intermediate increase in plasma total homocysteine (tHcy) causes coronary artery disease (CAD), the authors evaluated the number of coexisting major traditional risk factors, as well as the major tHcy determinants, in patients with the same degree of CAD but different tHcy levels.

MATERIALS AND METHODS

The authors studied 180 patients with CAD, who were divided into three groups according to tHcy levels: 60 patients with normal tHcy, 60 patients with moderate (15-30 micromol L(-1)) and 60 patients with intermediate hyperhomocysteinaemia (30-100 micromol L(-1)). The patient groups were matched for gender, age and number of affected coronary vessels. All patients were checked for the presence of traditional risk factors for CAD (i.e. hypertension, diabetes, hyperlipidaemia, smoking habit, familial history, obesity), as well as determinants of tHcy levels. The population was subdivided into those having, or not, a substantial burden of traditional risk factors (i.e. < 4 and > or = 4, respectively).

RESULTS

There was a significant trend towards a reduced number of subjects within the group with > or = 4 risk factors across increasing tHcy levels (51.7%, 37.8%, 26%, for normal, moderate, intermediate tHcy, respectively, chi2 for linear-trend = 0.006). Folate and vitamin B12 concentrations, estimated glomerular filtration rate (GFR), MTHFR 677C > T polymorphism were the major determinants of tHcy in this population.

CONCLUSIONS

In patients with the same degree of CAD, those with hyperhomocysteinaemia had a reduced burden of traditional risk factors as compared with those with normal tHcy levels. Hyperhomocysteinaemia was significantly associated with an emerging non-traditional risk factor such as lower GFR.

Combined calcium, magnesium and potassium supplementation for the management of primary hypertension in adults

BACKGROUND

Previous research suggests that increasing dietary intakes of calcium, potassium or magnesium separately may reduce BP to a small degree over the short term. It is unclear whether increasing intakes of a combination of these minerals produces a larger reduction in BP.

OBJECTIVES

To evaluate the effects of combined mineral supplementation as a treatment for primary hypertension in adults.

SEARCH STRATEGY

We searched the Cochrane Library, MEDLINE, EMBASE, Science Citation Index, ISI Proceedings, ClinicalTrials.gov, Current Controlled Trials, CAB abstracts, and reference lists of systematic reviews, meta-analyses and randomised controlled trials (RCTs) included in the review. The search was unrestricted by language or publication status.

SELECTION CRITERIA

Inclusion criteria were: 1) RCTs of a parallel or crossover design comparing oral supplements comprising a combination of potassium, and/or calcium, and/or magnesium with placebo, no treatment, or usual care; 2) treatment and follow-up >=8 weeks; 3) participants over 18 years old, with raised systolic blood pressure (SBP) >=140 mmHg or diastolic blood pressure (DBP) >=85 mmHg with no known primary cause; 4) SBP and DBP reported at end of follow-up. We excluded trials where participants were pregnant, or received antihypertensive medication which changed during the study.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and assessed trial quality. Disagreements were resolved by discussion or a third reviewer. Random effects meta-analyses and sensitivity analyses were conducted.

MAIN RESULTS

We included three RCTs (n=277) with between 24 and 28 weeks follow-up. Three combinations of minerals were investigated: potassium & magnesium, calcium & magnesium, and calcium & potassium. One trial investigated combinations of calcium & magnesium and of calcium & potassium, and for each found a statistically non-significant increase in both SBP and DBP. All three trials investigated the combination of potassium & magnesium. None of the trials provided data on mortality or morbidity. The combination of potassium & magnesium compared to control resulted in statistically non-significant reductions in both SBP (mean difference = -4.6 mmHg, 95% CI: -9.9 to 0.7) and DBP (mean difference = -3.8 mmHg, 95% CI: -9.5 to 1.8), although the results were heterogeneous (I(2)=68% and 85% for SBP and DBP respectively).A sensitivity analysis using alternative reported values which accounted for missing data had very little effect on DBP but resulted in a larger, statistically significant reduction in SBP (mean difference = -5.8 mmHg, 95% CI: -10.5 to -1.0). The quality of the trials was not well reported.

AUTHORS' CONCLUSIONS

We found no robust evidence that supplements of any combination of potassium, magnesium or calcium reduce mortality, morbidity or BP in adults. More trials are needed to investigate whether the combination of potassium & magnesium is effective.

Improvement in stroke mortality in Canada and the United States, 1990 to 2002

BACKGROUND

In the United States and Canada, folic acid fortification of enriched grain products was fully implemented by 1998. The resulting population-wide reduction in blood homocysteine concentrations might be expected to reduce stroke mortality if high homocysteine levels are an independent risk factor for stroke.

METHODS AND RESULTS

In this population-based cohort study with quasi-experimental intervention, we used segmented log-linear regression to evaluate trends in stroke-related mortality before and after folic acid fortification in the United States and Canada and, as a comparison, during the same period in England and Wales, where fortification is not required. Average blood folate concentrations increased and homocysteine concentrations decreased in the United States after fortification. The ongoing decline in stroke mortality observed in the United States between 1990 and 1997 accelerated in 1998 to 2002 in nearly all population strata, with an overall change from -0.3% (95% CI, -0.7 to 0.08) to -2.9 (95% CI, -3.5 to -2.3) per year (P=0.0005). Sensitivity analyses indicate that changes in other major recognized risk factors are unlikely to account for the reduced number of stroke-related deaths in the United States. The fall in stroke mortality in Canada averaged -1.0% (95% CI, -1.4 to -0.6) per year from 1990 to 1997 and accelerated to -5.4% (95% CI, -6.0 to -4.7) per year in 1998 to 2002 (P< or =0.0001). In contrast, the decline in stroke mortality in England and Wales did not change significantly between 1990 and 2002.

CONCLUSIONS

The improvement in stroke mortality observed after folic acid fortification in the United States and Canada but not in England and Wales is consistent with the hypothesis that folic acid fortification helps to reduce deaths from stroke.

Balancing benefits and harms in public health prevention programmes mandated by governments

Even when scientific evidence for a preventive health intervention is strong, many barriers exist to population-wide implementation

Oral Synthetic Folic Acid and Vitamin B12Supplements Work-If One Consumes Them

Oral supplements of synthetic folic acid and vitamin B12 are very effective in increasing blood levels of the vitamins and are known to prevent birth defects and cardiovascular diseases.

Scientific evidence supporting folic acid fortification of flour in Australia and New Zealand

BACKGROUND

Fortification of flour with folic acid is a safe, sustainable, and cost-effective approach for preventing spina bifida and anencephaly, and it is likely to confer multiple health benefits to the adult population. Scientists and advocates are bringing this intervention to the attention of policymakers in countries around the world, and consequently the demand for sound, science-backed policy rationale is increasing.

METHODS

We recently prepared this scientific review for scientists, physicians, and advocates who were promoting mandatory folic acid fortification of flour in Australia and New Zealand. This short document references the most relevant published scientific data and national and international recommendations from other countries and presents an argument for fortification based on demonstrated need, proven effectiveness, safety, and multiple health benefits.

CONCLUSIONS

With some modifications, this document could be utilized in other countries considering fortification of flour or other staple products with folic acid.

Intake of fruit and vegetables and the risk of ischemic stroke in a cohort of Danish men and women

BACKGROUND

Previous studies have suggested that a high dietary intake of fruit and vegetables is associated with a reduced risk of ischemic stroke. The magnitude of the effect is uncertain, and only one study reported data on the intake of specific fruit and vegetables and the risk of stroke.

OBJECTIVE

We examined whether the intake of fruit and vegetables is associated with a reduced risk of ischemic stroke, with particular attention paid to specific fruit and vegetables and subtypes of ischemic stroke.

DESIGN

In a prospective cohort study of 54,506 men and women who were included in the Danish Diet, Cancer, and Health study from 1993 to 1997, estimated total intakes of fruit and vegetables (in g/d) were extracted from a semiquantitative food-frequency questionnaire completed at baseline. Data about subjects hospitalized with ischemic stroke were obtained from the Danish National Registry of Patients and were verified later by record reviews. The follow-up for ischemic stroke ended on the date of a first hospital admission for stroke or transient ischemic attack, the date of death or emigration, or the end of the study, whichever came first.

RESULTS

We identified 266 cases of ischemic stroke involving hospitalization during 168,388 person-years of follow-up (median follow-up: 3.09 y; range: 0.02-5.10 y). After adjustment for potential confounders, persons in the top quintile of fruit and vegetable intake (median: 673 g/d) had a risk ratio of ischemic stroke of 0.72 (95% CI: 0.47, 1.12) relative to persons in the bottom quintile of intake (median: 147 g/d) (P for trend = 0.04). When comparing the top quintile with the bottom quintile, an inverse association was most evident for fruit intake (risk ratio: 0.60; 95% CI: 0.38, 0.95; P for trend = 0.02). Similar risk estimates were seen for most types of fruit and vegetables, although the risks were significant only for citrus fruit.

CONCLUSION

An increased intake of fruit may reduce the risk of ischemic stroke.

Cardiovascular risk factors, monitoring, and therapy for HIV-infected patients

Cardiovascular complications are important contributors to morbidity and mortality in HIV-infected patients. These complications can usually be detected at subclinical levels with monitoring, which can help guide targeted interventions. This article reviews available data on types and frequency of cardiovascular manifestations in HIV-infected patients and proposes monitoring strategies aimed at early subclinical detection. In particular, we recommend routine echocardiography for HIV-infected patients, even those with no evidence of cardiovascular disease. We also review preventive and therapeutic cardiovascular interventions. For procedures that have not been studied in HIV-infected patients, we extrapolate from evidence-based guidelines for the general population.

Nutritional supplementation with Chlorella pyrenoidosa for mild to moderate hypertension

Pharmacological treatment of hypertension reduces the risk of cardiovascular disease; however, randomized, controlled clinical trials and population studies have also shown that abnormally high blood pressure (BP) can be lowered with diet modification and exercise. The objective of this pilot study was to determine whether daily dietary supplementation with 10 g Chlorella tablets and 100 ml Chlorella extract for 2 months would reduce BP in subjects with a mean sitting diastolic BP (SiDBP) between 90 and 115 mm Hg. Thirty-three people were enrolled and underwent a 4-week washout period from all antihypertensive medications, during which they consumed placebo. At completion of this washout/placebo period, 24 subjects were considered evaluable (i.e., had a SiDBP between 90 and 115 mm Hg) and were continued in the study. After 1 or 2 months of dietary Chlorella supplementation, the average heart rate, sitting systolic BP, and SiDBP changed only slightly; after 2 months of Chlorella consumption, the group's mean SiDBP was 96.5 +/- 6.6. However, a heterogenous response pattern to Chlorella existed, with 25% (6/24) of the subjects achieving their BP goal (SiDBP less than 90 mm Hg). Furthermore, the BP of nonresponders did not increase significantly above washout values. Quality-of-life questionnaires indicated an overall perception that health had significantly improved in conjunction with Chlorella consumption. The results indicate that, for some subjects with mild to moderate hypertension, a daily dietary supplement of Chlorella reduced or kept stable their SiDBP.

Vitamin C as an antioxidant: evaluation of its role in disease prevention

Vitamin C in humans must be ingested for survival. Vitamin C is an electron donor, and this property accounts for all its known functions. As an electron donor, vitamin C is a potent water-soluble antioxidant in humans. Antioxidant effects of vitamin C have been demonstrated in many experiments in vitro. Human diseases such as atherosclerosis and cancer might occur in part from oxidant damage to tissues. Oxidation of lipids, proteins and DNA results in specific oxidation products that can be measured in the laboratory. While these biomarkers of oxidation have been measured in humans, such assays have not yet been validated or standardized, and the relationship of oxidant markers to human disease conditions is not clear. Epidemiological studies show that diets high in fruits and vegetables are associated with lower risk of cardiovascular disease, stroke and cancer, and with increased longevity. Whether these protective effects are directly attributable to vitamin C is not known. Intervention studies with vitamin C have shown no change in markers of oxidation or clinical benefit. Dose concentration studies of vitamin C in healthy people showed a sigmoidal relationship between oral dose and plasma and tissue vitamin C concentrations. Hence, optimal dosing is critical to intervention studies using vitamin C. Ideally, future studies of antioxidant actions of vitamin C should target selected patient groups. These groups should be known to have increased oxidative damage as assessed by a reliable biomarker or should have high morbidity and mortality due to diseases thought to be caused or exacerbated by oxidant damage.

Cardiovascular monitoring and therapy for HIV-infected patients

Cardiovascular complications are important contributors to morbidity and mortality in HIV-infected patients. These complications can usually be detected at subclinical levels with monitoring, which can help guide targeted interventions. This article reviews available data on types and frequency of cardiovascular manifestations in HIV+ patients and proposes monitoring strategies aimed at early subclinical detection. In particular, we recommend routine echocardiography for HIV+ patients, even those with no evidence of cardiovascular disease. We also review preventive and therapeutic cardiovascular interventions. For procedures that have not been studied in HIV+ patients, we extrapolate from evidence-based guidelines for the general population.

Multivitamin/mineral supplementation improves plasma B-vitamin status and homocysteine concentration in healthy older adults consuming a folate-fortified diet

Elevated homocysteine has been identified as an independent risk factor for cardiovascular and cerebrovascular disease. Although multivitamin use has been associated with low plasma homocysteine concentrations in several observational studies, no clinical trials have been conducted using multivitamin/mineral supplements to lower homocysteine. We determined whether a multivitamin/mineral supplement formulated at about 100% Daily Value will further lower homocysteine concentration and improve B-vitamin status in healthy older adults already consuming a diet fortified with folic acid. In this randomized, double-blind, placebo-controlled trial, 80 free-living men and women aged 50-87 y with total plasma homocysteine concentrations of > or =8 micromol/L received either a multivitamin/mineral supplement or placebo for 56 d while consuming their usual diet. After the 8-wk treatment, subjects taking the supplement had significantly higher B-vitamin status and lower homocysteine concentration than controls (P: < 0.01). Plasma folate, pyridoxal phosphate (PLP) and vitamin B-12 concentrations were increased 41.6, 36.5 and 13.8%, respectively, in the supplemented group, whereas no changes were observed in the placebo group. The mean homocysteine concentration decreased 9.6% in the supplemented group (P: < 0.001) and was unaffected in the placebo group. There were no significant changes in dietary intake during the intervention. Multivitamin/mineral supplementation can improve B-vitamin status and reduce plasma homocysteine concentration in older adults already consuming a folate-fortified diet.

Multivitamin use and mortality in a large prospective study

To determine the relation between multivitamin use and death from heart disease, cerebrovascular disease, and cancer, the authors examined a prospective cohort of 1,063,023 adult Americans in 1982-1989 and compared the mortality of users of multivitamins alone; vitamin A, C, or E alone; and multivitamin and vitamin A, C, or E in combination with that of vitamin nonusers by using multivariate Cox proportional hazard models. Multivitamin users had heart disease and cerebrovascular disease mortality risks similar to those of nonusers, whereas combination users had mortality risks that were 15% lower than those of nonusers. Multivitamin and combination use had minimal effect on cancer mortality overall, although mortality from all cancers combined was increased among male current smokers who used multivitamins alone (relative risk (RR) = 1.13, 95% confidence interval (CI): 1.05, 1.23) or in combination with vitamin A, C, or E (RR = 1.16, 95% CI: 1.06, 1.26), but decreased in male combination users who had never (RR = 0.86, 95% CI: 0.74, 0.99) or had formerly (RR = 0.90, 95% CI: 0.82, 0.98) smoked. No such associations were seen in women. These observational data provide limited support for the hypothesis that multivitamin use in combination with vitamin A, C, or E may reduce heart disease and cardiovascular disease mortality, but add to concerns raised by randomized studies that some vitamin supplements may adversely affect male smokers.

Intake of potassium, magnesium, calcium, and fiber and risk of stroke among US men

BACKGROUND

Animal experiments and epidemiological studies have suggested that high potassium intake may reduce the risk of stroke, but the evidence is inconclusive, and the role of other nutrients in potassium-rich foods remains unknown.

METHODS AND RESULTS

We examined the association of potassium and related nutrients with risk of stroke among 43 738 US men, 40 to 75 years old, without diagnosed cardiovascular diseases or diabetes, who completed a semiquantitative food frequency questionnaire in 1986. During 8 years of follow-up, 328 strokes (210 ischemic, 70 hemorrhagic, 48 unspecified) were documented. The multivariate relative risk of stroke of any type for men in the top fifth of potassium intake (median intake, 4.3 g/d) versus those in the bottom (median, 2.4 g/d) was 0.62 (95% CI, 0.43, 0.88; P for trend=0.007). Results for ischemic stroke alone were similar. Intakes of cereal fiber and magnesium, but not of calcium, were also inversely associated with risk of total stroke. These inverse associations were all stronger in hypertensive than normotensive men and were not materially altered by adjustment for blood pressure levels. Use of potassium supplements was also inversely related to risk of stroke, particularly among men taking diuretics (relative risk, 0.36; 95% CI, 0.18, 0.72).

CONCLUSIONS

Although these data do not prove a causal relationship, they are consistent with the hypothesis that diets rich in potassium, magnesium, and cereal fiber reduce the risk of stroke, particularly among hypertensive men. Potassium supplements may also be beneficial, but because of potential risks, use should be carefully monitored and restricted to men taking potassium-losing diuretics.

Chemoprevention of lung cancer: the rise and demise of beta-carotene

Beta-carotene and retinoids were the most promising agents against common cancers when the National Cancer Institute mounted a substantial program of population-based trials in the early 1980s. Both major lung cancer chemoprevention trials not only showed no benefit, but had significant increases in lung cancer incidence and in cardiovascular and total mortality. A new generation of laboratory research has been stimulated. Rational public health recommendations at this time include: 1. Five-A-Day servings of fruits and vegetables, a doubling of current mean intake; 2. systematic investigation of the covariates of extremes of fruit and vegetable intake; 3. discouragement of beta-carotene supplement use, due to adverse effects in smokers and no evidence of benefit in non-smokers; 4. multilevel research to develop and evaluate candidate chemoprevention agents to prevent lung and other common cancers; and 5. continued priority for smoking prevention, smoking cessation, and avoidance of known carcinogens in the environment.