Medical researchers sometimes explore the link between dietary interventions or supplements and disease in the hope of identifying substances that can ameliorate or prevent illness. Several new studies undertaken with just that goal, however, have come up empty handed.
One study, published online as two separate articles in the New England Journal of Medicine, looked at whether vitamin D or omega-3 fatty acids were protective against cancer or cardiovascular disease (CVD). In another, researchers reviewed studies of patients with heart failure to see if they benefited from reduced dietary salt.
Both vitamin D and fish oil supplementation have become common in recent years, yet studies of their health effects are inconclusive. A nationwide placebo-controlled trial enrolled nearly 26,000 people, including men ages 50 or older and women 55 or older. They were randomly assigned to receive vitamin D3 2,000 IU daily or marine n-3 (also called omega-3) fatty acids 1 g daily (both supplements) or a placebo. They were followed for an average of 5.3 years to compare rates of new invasive cancers or cardiovascular events, including mortality, among the randomized groups. Neither vitamin D supplementation nor marine n-3 supplementation was associated with a lower risk of developing cancer or a cardiovascular event. Limitations of the cancer study noted by the authors were the duration of follow-up-5.3 years-and that only one dose of vitamin D was tested.
The dietary salt study was undertaken because patients with heart failure are routinely advised to reduce salt intake in keeping with several international cardiovascular guidelines. The guidelines, however, lack support from high-quality evidence, and some studies have suggested that salt restriction may actually harm patients with heart failure. In this study, researchers systematically reviewed all randomized clinical trials of salt reduction in patients with heart failure and identified nine relevant studies involving 479 patients. No high-quality evidence was found in these studies to support reducing dietary salt. Salt reduction didn't demonstrably improve cardiovascular mortality or myocardial infarction rates.
Further research into preventive therapies for cancer and CVD is needed.-Joan Zolot, PA
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