Background
Seaweed has been a very important part of the Japanese diet for many centuries and is an important source of fiber, minerals, vitamins, polysaccharides, and iodine. Seaweed is a rich source of bioactive metabolites, and compounds found in it have various biological activities including anticoagulant, anti-viral, antioxidant, anti-allergic, anti-cancer, anti-inflammatory, anti-obesity, and neuroprotective properties [
1]. Nevertheless, epidemiological information concerning the effects of seaweed consumption has been scarce. Inverse associations have been reported between seaweed consumption and stomach cancer [
2], colorectal cancer [
3], allergic rhinitis [
4], mortality from all causes, pancreatic cancer, lung cancer, kidney cancer, and cerebrovascular disease [
5], breast cancer [
6], and elevated blood pressure [
7], while positive associations have been shown between seaweed consumption and prostate cancer [
8], upper aerodigestive tract cancer [
9], mortality from colon cancer [
5], metabolic syndrome [
10], and thyroid cancer [
11].
Several lines of laboratory studies have provided insight into the neuroprotective effects of seaweed, suggesting that seaweed consumption might affect depressive symptoms in humans [
1]. To our knowledge, there has been no epidemiological evidence regarding the relationship between seaweed consumption and depression. The current cross-sectional study aimed to investigate the association between seaweed consumption and depressive symptoms during pregnancy in Japanese women using baseline data from the Kyushu Okinawa Maternal and Child Health Study (KOMCHS).
Results
The prevalence of depressive symptoms during pregnancy was 19.3% among the 1745 pregnant women. The mean age of the subjects and gestation at baseline were 31.2 years and 18.5 weeks, respectively (Table
1). About 5% of the subjects had a personal history of depression and 10% had a family history of depression. Mean daily total energy consumption and mean daily energy-adjusted seaweed consumption during pregnancy were 7434.2 kJ and 12.3 g, respectively.
Table 1
Distribution of selected characteristics in 1745 pregnant women
Age, years, mean ± SD | 31.2 ± 4.3 |
Gestation, weeks, mean ± SD | 18.5 ± 5.4 |
Region of residence | |
Fukuoka Prefecture | 971 (55.6) |
Other than Fukuoka Prefecture in Kyushu | 592 (33.9) |
Okinawa Prefecture | 182 (10.4) |
Number of children | |
0 | 703 (40.3) |
1 | 690 (39.5) |
≥ 2 | 352 (20.2) |
Nuclear family structure | 1474 (84.5) |
History of depression | 84 (4.8) |
Family history of depression | 175 (10.0) |
Having ever smoked | 563 (32.3) |
Ever experiencing secondhand smoke exposure at home | 1315 (75.4) |
Ever experiencing secondhand smoke exposure at work | 1106 (63.4) |
Job typea
| |
Unemployed | 705 (40.4) |
Professional or technical | 435 (24.9) |
Clerical or related occupation | 328 (18.8) |
Sales | 83 (4.8) |
Service | 115 (6.6) |
Production | 51 (2.9) |
Othersb
| 28 (1.6) |
Household income, yen/year | |
< 4,000,000 | 632 (36.2) |
4,000,000 − 5,999,999 | 618 (35.4) |
≥ 6,000,000 | 495 (28.4) |
Education, years | |
< 13 | 428 (24.5) |
13 − 14 | 577 (33.1) |
≥ 15 | 740 (42.4) |
Body mass index, kg/m2, mean ± SD | 21.4 ± 2.8 |
Daily nutrient intakec
| |
Total energy, kJ, mean ± SD | 7434.2 ± 2057.0 |
Seaweed, g, mean ± SD | 12.3 ± 12.7 |
Fish, g, mean ± SD | 46.7 ± 25.8 |
Yogurt, g, mean ± SD | 34.8 ± 39.5 |
Table
2 shows the distributions of confounding factors according to seaweed consumption. Seaweed consumption was positively associated with age, professional or technical occupation, and consumption of fish and yogurt and inversely with active smoking status, clerical or related occupation, and sales occupation.
Table 2
Characteristics according to quartile of seaweed consumption in 1745 pregnant women
Age, years, mean | 30.8 | 31.1 | 31.6 | 31.3 | 0.04 |
Gestation, weeks, mean | 18.5 | 18.4 | 18.5 | 18.7 | 0.67 |
Region of residence, % | | | | | 0.31 |
Fukuoka Prefecture | 56.4 | 59.2 | 54.1 | 52.9 | |
Other than Fukuoka Prefecture in Kyushu | 34.6 | 30.7 | 36.0 | 34.3 | |
Okinawa Prefecture | 8.9 | 10.1 | 9.9 | 12.8 | |
Number of children, % | | | | | 0.77 |
0 | 39.2 | 42.0 | 37.4 | 42.6 | |
1 | 39.2 | 39.0 | 44.7 | 35.2 | |
≥ 2 | 21.6 | 19.0 | 17.9 | 22.2 | |
Nuclear family structure, % | 85.8 | 83.9 | 85.8 | 82.4 | 0.28 |
History of depression, % | 5.5 | 4.8 | 4.4 | 4.6 | 0.48 |
Family history of depression, % | 10.3 | 11.5 | 8.7 | 9.6 | 0.45 |
Having ever smoked,% | 37.2 | 36.0 | 27.1 | 28.8 | 0.0007 |
Ever experiencing secondhand smoke exposure at home, % | 78.2 | 76.6 | 72.5 | 74.1 | 0.08 |
Ever experiencing secondhand smoke exposure at work, % | 64.9 | 64.5 | 62.2 | 62.0 | 0.29 |
Job typeb, % | | | | | 0.03 |
Unemployed | 38.1 | 41.7 | 40.8 | 41.0 | |
Professional or technical | 21.1 | 23.6 | 28.0 | 27.0 | |
Clerical or related occupation | 22.7 | 17.0 | 17.9 | 17.6 | |
Sales | 6.0 | 4.6 | 5.1 | 3.4 | |
Service | 6.7 | 7.6 | 5.5 | 6.6 | |
Production | 3.9 | 3.9 | 1.6 | 2.3 | |
Othersc
| 1.6 | 1.6 | 1.2 | 2.1 | |
Household income, yen/year, % | | | | | 0.11 |
< 4,000,000 | 41.3 | 35.6 | 32.3 | 35.7 | |
4,000,000 − 5,999,999 | 33.3 | 35.8 | 34.9 | 37.8 | |
≥ 6,000,000 | 25.5 | 28.7 | 32.8 | 26.5 | |
Education, years, % | | | | | 0.10 |
< 13 | 28.0 | 23.9 | 23.2 | 23.1 | |
13 − 14 | 31.9 | 32.3 | 36.7 | 31.4 | |
≥ 15 | 40.1 | 43.8 | 40.1 | 45.5 | |
Body mass index, kg/m2, mean | 21.7 | 21.4 | 21.4 | 21.4 | 0.11 |
Fish, g, meand
| 40.3 | 45.7 | 49.2 | 51.8 | < 0.0001 |
Yogurt, g, meand
| 32.4 | 32.4 | 36.4 | 38.1 | 0.01 |
Table
3 gives ORs and 95% CIs for depressive symptoms during pregnancy by quartiles of seaweed consumption. Compared with seaweed consumption in the lowest quartile, consumption in the second, third, and fourth quartiles was significantly associated with a lower prevalence of depressive symptoms during pregnancy, showing a clear inverse linear trend in crude analysis. After adjustment for age; gestation; region of residence; number of children; family structure; history of depression; family history of depression; smoking; secondhand smoke exposure at home and at work; job type; household income; education; body mass index; and consumption of fish and yogurt, the inverse association was slightly attenuated but remained statistically significant: the adjusted ORs (95% CIs) for depressive symptoms during pregnancy in the first, second, third, and fourth quartiles of seaweed consumption were 1 (reference), 0.72 (0.51 − 1.004), 0.71 (0.50 − 1.01), and 0.68 (0.47 − 0.96), respectively (
P for trend = 0.03).
Table 3
Odds ratios (ORs) and 95% confidence intervals (CIs) for depressive symptoms during pregnancy by quartiles of seaweed consumption in 1745 pregnant women
Intake, g/daya
| 2.4 | 5.6 | 12.6 | 28.6 | |
Depressive symptoms, %b
| 24.8 | 18.8 | 17.0 | 16.5 | |
Crude OR (95% CI) | 1.00 | 0.70 (0.51 − 0.97) | 0.62 (0.45 − 0.86) | 0.60 (0.43 − 0.83) | 0.002 |
Adjusted OR (95% CI)c
| 1.00 | 0.72 (0.51 − 1.004) | 0.71 (0.50 − 1.01) | 0.68 (0.47 − 0.96) | 0.03 |
Discussion
The current cross-sectional study revealed that, after adjustment for potential dietary and non-dietary confounding factors, higher seaweed consumption was independently associated with a lower prevalence of depressive symptoms during pregnancy. To the best of our knowledge, this study is the first to demonstrate the association between seaweed consumption and depressive symptoms.
The observed inverse association between seaweed consumption and depressive symptoms may be attributable to the neuroprotective properties of seaweed [
1]. Yan
et al. reported that Hijiki (
Hijikia fusiformis) showed the strongest 1-diphenyl-2-picryl hydrazyl radical scavenging activity, followed by Wakame (
Undaria pinnatifida), and that fucoxanthin, a major antioxidant, was the richest carotenoid in Hijiki [
20]. Sangeetha
et al. demonstrated that fucoxanthin had greater potential than β-carotene to modulate lipid perioxidation as well as the activity of catalase and glutathione transferase in the plasma and livers of retinol-deficient rats [
21]. With respect to the anti-inflammatory properties of seaweed, dieckol, a compound isolated from the marine brown alga
Ecklonia cava, significantly inhibited the release of nitric oxide, prostaglandin E
2, interleukin-1β, and tumor necrosis factor-α in lipopolysaccharide-stimulated murine BV2 microglial cells via the down-regulation of nuclear factor-κB and p38 mitogen-activated protein kinase activation [
22]. Alternatively, the other ingredients in seaweed may be preventive against depressive symptoms. For example, a significant inverse association between calcium intake and depression was found in two studies of Korean women [
23,
24]. In the present study’s population, higher calcium intake was likewise significantly inversely related to the prevalence of depressive symptoms during pregnancy [
19]. A systematic review concluded that higher magnesium intake also seemed to be associated with lower depressive symptoms [
25].
The overall diet patterns of subjects who regularly eat seaweed may also be responsible for the observed inverse association. In the Japan Public Health Center-based Prospective Study, a prudent dietary pattern characterized by a high intake of vegetables, fruit, soy products, potatoes, seaweed, mushrooms, and fish was significantly associated with a reduced risk of suicide in both men and women [
26]. Depression being a major precondition of suicide, this may indicate that diet health is inversely related to the severity of depressive symptoms.
Some methodological limitations of the present study warrant mention. The cross-sectional nature of the present study hampers the drawing of conclusions about causality.
Our DHQ could only approximate consumption and was designed to assess dietary intake for one month prior to completing the questionnaire. The present study subjects participated in the baseline survey at various points between the 5th and 39th week of pregnancy. The possibility of non-differential exposure misclassification would have biased the estimates of the observed association towards the null.
Depressive symptoms were assessed using the CES-D scale rather than structured diagnostic interviews. The CES-D includes questions on physical symptoms such as fatigue and physical discomfort, which are also typical complaints of pregnancy; the consequence of this symptom overlap could have been an overestimation of depression. The prevalence of depressive symptoms in this study was, however, lower than that in a representative sample of the Japanese general population: the prevalence of depressive symptoms (CES-D score of ≥ 16) was 30.7% in 2315 women aged 30–39 years [
27]. Again, our study subjects took part in the baseline survey at various points between the 5th and 39th week of pregnancy. Therefore, it is difficult to accurately estimate the incidence and prevalence of depressive symptoms during pregnancy. The possibility of non-differential outcome misclassification would have given rise to an underestimation of our results.
We could not calculate the participation rate because we do not have exact figures for the number of pregnant women who were provided with a set of leaflets explaining the KOMCHS, an application form, and a self-addressed and stamped return envelope by the 423 collaborating obstetric hospitals. We were not able to assess the differences between participants and non-participants because information on personal characteristics such as age, socioeconomic status, and history of depression was not available for non-participants. Our subjects were probably not representative of Japanese women in the general population, however. For example, a population census conducted in 2000 in Fukuoka Prefecture found that the percentages of women aged 30 to 34 years with < 13, 13–14, ≥ 15, and an unknown number of years of education were 52.0%, 31.5%, 11.8%, and 4.8%, respectively [
28]. The corresponding figures for this study were 24.5%, 33.1%, 42.4%, and 0.0%, respectively. Thus, our study subjects were more educated and probably more aware of health topics than women in the general population.
Although adjustment was made for several dietary and non-dietary confounding factors, residual confounding effects could not be ruled out.
Acknowledgements
The authors would like to thank the Kyushu Branch of the Japan Allergy Foundation, the Fukuoka Association of Obstetricians & Gynecologists, the Okinawa Association of Obstetricians & Gynecologists, the Miyazaki Association of Obstetricians & Gynecologists, the Oita Association of Obstetricians & Gynecologists, the Kumamoto Association of Obstetricians & Gynecologists, the Nagasaki Association of Obstetricians & Gynecologists, the Kagoshima Association of Obstetricians & Gynecologists, the Saga Association of Obstetricians & Gynecologists, the Fukuoka Society of Obstetrics and Gynecology, the Okinawa Society of Obstetrics and Gynecology, the Fukuoka City Government, and the Fukuoka City Medical Association for their valuable support.
This research was supported by JSPS KAKENHI Grant Numbers 19590606, 20791654, 21590673, 22592355, 22119507, 24390158, 25463275, and 25670305, by Health and Labour Sciences Research Grants for Research on Allergic Disease and Immunology and Health Research on Children, Youth and Families from the Ministry of Health, Labour and Welfare, Japan, by Meiji Co. Ltd., and by the Food Science Institute Foundation.
Competing interests
YM and KT were financially supported by Meiji Co. Ltd. The other authors have no conflict of interest.
Authors’ contributions
YM, KT, and MA contributed to the study concept and design and the acquisition of data. HO and SS were responsible for the estimation of dietary factors. YM was responsible for the analysis and interpretation of data and the drafting of the manuscript. All authors read and approved the final manuscript.