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Sleep patterns, docosahexaenoic acid, and gestational length

Department of Pharmacology
The Danish University of Pharmaceutical Sciences
Universitetsparken 2
DK-2100 Copenhagen
Denmark
E-mail: hsh{at}dfh.dk

Sjúrur FróI Olsen

Maternal Nutrition Group
Danish Epidemiology Science Centre
Statens Serums Institut
Copenhagen
Denmark

Dear Sir:

It was with great interest that we read in the Journal the recent article by Cheruku et al (1), which indicated that the maternal plasma docosahexaenoic acid (DHA) concentration during pregnancy is positively correlated with a more mature neonatal sleep-state pattern. The study involved 17 women who were divided into 2 groups (high-DHA group, n = 10; low-DHA group, n = 7) on the basis of the percentage of DHA in their plasma phospholipids. The sleep patterns of the infants in the 2 groups were analyzed by analysis of variance, and maternal age and education were tested as covariates and found to be nonconfounding. The authors suggest that "differences in the prenatal supply of LCPUFAs [long-chain polyunsaturated fatty acids], especially DHA, may modify brain phospholipids and affect neural function." We agree that this is a plausible suggestion because DHA is very important for brain function (2), but at the same time we believe that increased gestational length may also be responsible for the findings of Cheruku et al, assuming that longer gestation will also lead to a more mature central nervous system.

We previously showed that the dietary intake of fish oil containing DHA and eicosapentaenoic acid by pregnant women can prolong gestation and increase birth weight (3). As expected in the study by Cheruku et al, it is evident from Table 1 of their article that the high-DHA group tended to have a longer gestation, to have infants with higher birth weights, and to have infants who were longer in length at birth. None of these variables were significantly different from those of the low-DHA group, but this was also to be expected because of the low number of subjects.

We therefore wondered whether the observed association between DHA and sleep patterns might, in part or even fully, be mediated through a prolonging effect of DHA on gestation. This contention can be easily tested by examining 2 associations: 1) whether sleep patterns correlate with length of gestation and 2) whether the association between DHA and sleep patterns is weakened, or even abolished, when length of gestation is adjusted for by including the variable as a covariate in the analysis of variance. A condition for making these analyses in an optimal way is that gestation length, an inherently imprecise variable, is assessed with reasonable precision. Information on how gestation length is assessed is therefore needed to enable full evaluation of the results.

REFERENCES

1. Cheruku SR, Montgomery-Downs HE, Farkas SL, Thoman EB, Lammi-Keefe CJ. Higher maternal plasma docosahexaenoic acid during pregnancy is associated with more mature neonatal sleep-state patterning. Am J Clin Nutr 2002;76:608-13.[Abstract/Free Full Text]
2. Lauritzen L, Hansen HS, Jorgensen MH, Michaelsen KF. The essentiality of long chain n-3 fatty acids in relation to development and function of the brain and retina. Prog Lipid Res 2001;40:1-94.[Medline]
3. Olsen SF, Sorensen JD, Secher NJ, et al. Randomised controlled trial of effect of fish-oil supplementation on pregnancy duration. Lancet 1992;339:1003-7.[Medline]

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