Conflicting findings confuse consumers. What should you do now?
Consumers worried about dietary sodium and who are watching their salt intake might find their blood pressure rising over a recent flurry of apparently conflicting studies. The ink was hardly dry on a review headlined as questioning the association between salt and heart disease when another new study again fingered salt as a killer.
First, a systematic analysis of the scientific evidence for the Cochrane Review concluded, Giving advice on cutting down on the amount of salt has no clear benefits in terms of likelihood of dying or experiencing cardiovascular disease. Based on data from six clinical trials totaling some 6,000 adults with normal or high blood pressure, the review found no clear evidence that reducing salt intake to lower dietary sodium cuts the risk of death from heart disease or any other cause in people with normal or high blood pressure. A Cochrane press release flatly summarized, Cutting down on salt does not reduce your chance of dying.
Overall, those who reduced their salt intake did see a lower risk of cardiovascular events, but the difference wasnt statistically significant. Lower salt consumption was also linked to a small reduction in blood pressure. One trial found that cutting down on salt was actually linked to a greater risk of dying among 341 patients with congestive heart failure.
Writing in the American Journal of Hypertension, Rod S. Taylor, PhD, of Peninsula College of Medicine and Dentistry, University of Exeter in England, and colleagues explained their review: Our estimates of benefits from dietary salt restriction are consistent with the predicted small effects on clinical events attributable to the small blood pressure reduction achieved. A previous Cochrane Review had found salt reduction does lower blood pressure, but only an average 1.1/0.6 mm Hg.
Even that link was recently challenged by a controversial Belgian study (see the August 2011 Health & Nutrition Letter) reporting that, among participants initially without high blood pressure, there was no association between sodium levels and risk of developing the condition.
The American Heart Association responded to both studies by saying that its sticking to its advice to slash sodium intake to 1,500 milligrams daily or less. A spokesperson added, Reducing sodium now-even for people who have normal blood pressure-can reap enormous long-term benefits.
And a second analysis of the Cochrane Review data, published only weeks later in The Lancet, claimed that the original findings were incorrect. The re-analysis found that a reduction of 2,000 milligrams of daily salt intake-800 milligrams of sodium- would lead to a 20% drop in the risk of heart attack and stroke.
Even the authors of the original Cochrane analysis seemed to distance themselves from the headlines over their findings. Taylor cautioned, The important thing to note is that our results dont say that asking people to reduce their salt intake is not a good thing for their health, but rather giving advice on reducing salt alone is not enough.
- Potassium Powerhouses
A new study suggests that higher dietary intake of potassium is linked to lower risk of death from heart disease. While cutting back on sodium, consider boosting potassium with these foods:- Sweet potatoes
- Tomato paste, puree, juice, sauce
- Potatoes
- White beans
- Yogurt (low- or non-fat)
- Prunes and prune juice
- Halibut
- Soybeans
- Tuna
- Lima beans
- Winter squash
- Bananas
- Spinach
Indeed, those headlines (Putting Down the Salt Shaker May Not Help the Heart) were followed almost immediately by the publication of a large population-based study linking high sodium intake to greater risk of death from all causes. Quanhe Yang, PhD, of the CDC, and colleagues analyzed data on 12,267 adults who reported one days diet in the National Health and Nutrition Examination Survey (NHANES). Each 1,000-milligram daily increase in sodium intake was linked to a 20% greater risk of all-cause mortality.
An earlier NHANES analysis had found only an insignificant association between sodium and cardiovascular death. This study, however, had a longer follow-up-nearly 15 years-and incorporated a validated method developed by the National Cancer Institute to estimate the usual intakes of sodium and potassium.
How to make sense of all these dueling salt studies? Alice H. Lichtenstein, DSc, director of Tufts HNRCA Cardiovascular Nutrition Laboratory, advises, Mean change in blood pressure is not what is important; what is important is whether an individual keeps their blood pressure in a normal range. For many people cutting sodium intake will have a significant effect, without side effects that may occur with antihypertensive drugs.
Hence, if someone is told they have high blood pressure, the first thing they should do is cut their sodium intake and have it re-checked by their doctor. If that does not get them into the normal range they should talk to a dietitian to ensure they are actually cutting their sodium intake, make appropriate changes, and then have their blood pressure re-checked. It is easy to miss hidden sodium in common foods. If they still have elevated blood pressure they should then discuss other options with their doctor.
The CDC study also spotlighted the potential importance of dietary potassium as a counterweight to sodium. Each 1,000-milligram increase in potassium intake was associated with a 20% lower mortality risk, and higher potassium was linked to lower rates of cardiovascular and heart-disease death. Moreover, a high ratio of sodium to potassium intake was connected to higher mortality risk.
Yang and colleagues concluded, Public health recommendations should emphasize simultaneous reduction in sodium intake and increase in potassium intake.
But Tufts Lichtenstein cautions, You cant just go with the ratio. Theres no data to show that not cutting sodium while taking a potassium pill to improve the ratio is equivalent to cutting sodium.
You can, however, cut back on processed foods-the leading source of dietary sodium-and eat more fresh fruits and vegetables, which are excellent sources of potassium. (See box.) Thats a health-savvy approach regardless of how the science shakes out.
TO LEARN MORE: American Journal of Hypertension, August 2011; abstract at dx.doi.org/10.1038/ajh.2011.115. Archives of Internal Medicine, July 11, 2011; abstract at archinte.ama-assn.org/cgi/content/short/171/13/1183.