Deep-sea fish oil and vitamin D are a kind of health products that many people are eating. In recent years, the publicity of deep-sea fish oil has also been very popular. From whitening skin to improving memory to preventing diseases such as cancer and cardiovascular diseases, it can be described as "universal oil".
But do these health products really have such a magical effect?
Recently, two studies and an editorial published in the top medical journal New England Journal of Medicine have fully demonstrated that dietary fish oil and vitamin D supplementation does not reduce cancer and cardiovascular disease morbidity and mortality.
1, the long-popular "myth of health products"
The use of dietary supplement products is common in the United States.The National Health and Nutrition Examination Survey conducted from 1999 to 2012 showed that more than half of American adults consumed dietary supplements.Over the last decade, the number of people supplemented with fish oil and vitamin D has increased 10-fold and 4.1 times, but the long-term health benefits of these products remain questionable.
In the late 1990s, an open-label Italian Study Group on Survival in Myocardial Infarction – Preventive Trial data demonstrated that n-3 fatty acids (commonly known as omega-3 fatty acids) in deep-sea fish oil can protect against coronary heart disease.Based on the results of this trial, the American Heart Association recommends omega-3 fatty acids for secondary prevention of coronary heart disease.Since then, for quite some time, omega-3 fatty acids have been used as a preventive measure against recurrence after coronary heart disease.However, as more and more large randomized trials have demonstrated, supplementation with omega-3 fatty acids has no consistent effect on reducing the incidence of cardiovascular events in people at high risk of coronary heart disease.After a large meta-analysis, the American Heart Association updated the previous guidelines.The new guidelines state that the use of omega-3 fatty acids is reasonable but not recommended.
Despite this, the "magical effect" of deep-sea fish oil is quite deeply rooted.In addition, although omega-3 fatty acids do not prevent relapse after cardiovascular disease occurs, what if they are used for disease prevention before the disease occurs?The test data on this is still blank.
Similar to findings with omega-3 fatty acids, a large body of observational data suggests that the lower the vitamin D content, the higher the risk of cancer.These studies, in turn, highlight the need to implement RCTs.
2, a trial with two heavy outcomes
To address these doubts, the investigators conducted a nationwide, randomized, placebo-controlled trial called "VITAL" with a 2 × 2 factorial design in which men aged 50 years and older and women aged 55 years and older were given 2000 IU of vitamin D3 (cholecalciferol) and 1 g of marine omega-3 fatty acids daily to assess the effect of preventing cancer and cardiovascular disease, with a median follow-up.5Three years, a total of 25,871 volunteers participated in the study (including 5,106 blacks).
The primary endpoint of the study was any type of invasive cancer and major cardiovascular events (composite of myocardial infarction, stroke, or death from cardiovascular causes).Secondary endpoints included site-specific cancer, cancer death, and other cardiovascular events.The results of the study showed that:
In the omega-3 fatty acid trial, 386 participants and 419 in the placebo group had major cardiovascular events (hazard ratio, 0.92); 820 participants and 797 in the placebo group with a diagnosis of invasive cancer (hazard ratio, 1.03).In the analysis of the key secondary end points, the risk was described as follows: for the extended composite of cardiovascular events, the hazard ratio was 0. 5.93; total myocardial infarction, hazard ratio 0.72; total stroke, hazard ratio 1.04; death due to cardiovascular causes, hazard ratio 0.96; and death from cancer (341 deaths from cancer), hazard ratio 0.97. Death from any cause (total 978 deaths), hazard ratio 1.02. No risk of bleeding or other serious adverse events was observed.
These data are generally consistent with those of the recent ASCEND, a study of cardiovascular events in diabetes.The study showed that the use of omega-3 fatty acids did not have any effect on the primary prevention of cardiovascular disease in diabetic patients.
In the vitamin D trial, a total of 1,617 participants had a diagnosis of cancer (793 in the vitamin D group and 824 in the placebo group; hazard ratio 0.96).One major cardiovascular event occurred in 805 participants (396 in the vitamin D group and 409 in the placebo group; hazard ratio 0.97).
In the analysis of secondary endpoints, the risk is as follows: cancer death (341 deaths) is 0.83; for breast cancer 1.02; 0 for prostate cancer.88; colorectal cancer as 1.09; extended composite endpoint for major cardiovascular events plus coronary revascularization was 0.96; for myocardial infarction is 0.96; stroke is 0.95; for death from cardiovascular causes 1.11. In the analysis of deaths from any cause (978 deaths), the hazard ratio was 0. 1.99. No risk of hypercalcemia or other adverse events was found.
This trial is one of the largest and longest randomized trials testing whether vitamin D supplementation prevents cardiovascular disease or cancer.A three-year randomized placebo-controlled trial in New Zealand, the Vitamin D Assessment Study (VIDA), in which 5,110 patients received monthly high-dose vitamin D supplementation (100,000 IU), also demonstrated no effect of vitamin D supplementation on major cardiovascular events and the incidence of cancer.
Overall, supplementation with omega-3 fatty acids and vitamin D did not reduce the incidence of invasive cancer or cardiovascular events compared with placebo.
3, and the trial results are directly applicable to most patients
For this trial, John F.Dr Keaney wrote in the editorial, "There are several points worth noting in this trial.First, the large number of participants and the fact that a significant proportion of the participants were black make this cohort study more representative.In this case, the results of this trial should be directly applicable to the majority of patients.Second, although the median serum 25-hydroxyvitamin D level at baseline was 30 per milliliter.8 ng, but approximately 1 in 13 participants had serum 25-hydroxyvitamin D levels below 20 ng per mL.Even in this subgroup, vitamin D supplementation had no effect on the number of cases of any type of invasive cancer.Therefore, vitamin D supplementation is not good for health over a wide range of serum vitamin D levels.
Keaney believes that in the absence of other convincing data, the cautious conclusion is that dietary supplementation with omega-3 fatty acids or vitamin D is not an ideal strategy to prevent cardiovascular events or cancer.
1.n − 3 Fatty Acids and Cardiovascular Disease and Cancer
2.Vitamin D and Cancer and Cardiovascular Disease
3.VITAL Signs for Dietary Supplementation to Prevent Cancer and Heart Disease