| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
LETTER TO THE EDITOR |
Graduate Center for Nutritional Sciences
University of Kentucky
Lexington, KY 40506-0054
E-mail: ckchow{at}uky.edu
Dear Sir:
In a recent issue of the Journal, Ravaglia et al (1) reported that higher plasma concentrations of some forms of vitamin E were associated with a higher risk of cognitive impairment in an elderly Italian cohort. The population-based study, which aimed to investigate epidemiologic and risk factors for cognitive impairment, was properly designed and carried out, and the results obtained are interesting. However, several issues in this article, which could profoundly affect the interpretation of the data obtained, need clarification.
The first such issue is the unit of expression for plasma tocopherols and their oxidation products. Plasma (or serum) tocopherol concentration has been reported as µg, mg, µmol, or mmol per mL or L of plasma, with or without adjustment for per unit of lipid, triglyceride, or cholesterol (or all 3). Nagaya et al (2) compared various indexes for vitamin E status in health subjects and concluded that the ratio of serum vitamin E to total triglyceride plus total cholesterol is the simplest and most appropriate index for serum vitamin E status when serum fatty acid composition is not analyzed. On the basis of the data obtained from routine analysis, Ford et al (3) reported that ratios of vitamin E to cholesterol can be used to better define the vitamin E status of patients with disease states or disorders that are likely to increase LDL-cholesterol concentrations, such as cholestasis. They also reported that measurement of serum vitamin E concentration alone is sufficient to establish a patient's vitamin E status. As is shown in Table 1
in the article by Ravaglia et al (page 1309), the concentration of serum cholesterol in subjects with dementia (5.7 ± 1.3 mmol/L) is significantly lower than that in the subjects with normal cognition (6.2 ± 1.1 mmol/L) or mild cognitive impairment (6.2 ± 1.2 mmol/L). Therefore, the rationale for expressing the plasma concentrations of tocopherols and their oxidation products per unit of serum cholesterol should be provided.
|
-tocopheryl quinone and 5-nitro-
-tocopherol in these persons are significantly higher than those in the other 2 groups when the data are adjusted for cholesterol. As is shown in Table 1
here, when data are expressed in mmol/L, the mean concentrations of tocopherols, -tocopheryl quinine, and 5-nitro--tocopherol (the values are obtained by multiplying cholesterol-adjusted tocopherol concentrations by the cholesterol concentrations of respective groups) in the plasma are similar among the 3 subject groups.
Another issue that needs clarification is the concentrations of -tocopheryl quinine and 5-nitro--tocopherol. -Tocopherol is well recognized as the dominant form of plasma vitamin E. In addition, the plasma or tissue concentrations of -tocopheryl quinone (4, 5) and 5-nitro--tocopherol (6, 7) reported by others are only a small fraction of -tocopherol or are not detectable. Thus, the higher plasma concentration of -tocopheryl quinone than of -tocopherol and the high plasma concentration of 5-nitro--tocopherol reported by Ravaglia et al are a surprise. It is not clear how the plasma concentrations of -tocopheryl quinone and 5-nitro--tocopherol were measured and whether their values are presented on the same basis as the values of -tocopherol.
The importance of plasma tocopherols in relation to other characteristics of the subjects studied is another concern. In addition to serum cholesterol, several of the characteristics of subjects, including age, sex, years of education, Mini-Mental State Examination score, current smoking, stroke, body mass index, and sedentary lifestyle, are significantly associated with cognitive status or dementia (see Table 1 in Ravaglia et al). Moreover, the concentrations of some tocopherols and their oxidation products are significantly associated with cognitive status or dementia only when the data are adjusted for cholesterol. It is not clear why Ravaglia et al singled out plasma tocopherols and their oxidation products, rather than other characteristics of subjects, as predictors for the risk of cognitive impairment.
Reports dealing with the association between the intake or status of a nutrient or dietary component and the risk of chronic diseases often command high attention. Readers and the scientific community as a whole can benefit from a thorough evaluation and cautious interpretation of data obtained through investigations.
ACKNOWLEDGMENTS
The author had no personal or financial conflict of interest.
REFERENCES
-tocopherol-C14 in the rat and chicken. J Lipid Res 1963;4:330–6.[Abstract]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
