Dietary supplements are often used by the elderly to improve their nutritional status. However, intake above the recommended dietary levels may be detrimental, and uncertainty exists on the potential health benefits of supplementation in this population. The aim of this study was to describe supplement use among Icelandic older adults and to assess its association with total mortality and CVD-related mortality. This study used data from the Age Gene/Environment Susceptibility-Reykjavik study, which recruited 5764 participants aged 66–98 years in 2002–2006. Intake of vitamins and minerals from dietary supplements was estimated from interviews. Hazard ratios (HR) for mortality were estimated in multivariate analyses with follow-up ending in 2009. The results showed that most (77 %) of the participants used supplements. Overall, the consumption of vitamins and minerals from supplements was moderate although 22 and 14 % of users exceeded the upper recommended intake levels for vitamin B6 and Zn, respectively. Supplement users followed in general a healthier lifestyle than non-users. There were 1221 deaths including 525 CVD-related deaths during the follow-up period. When comparing multivitamin users with non-users in multivariable models, no associations with total mortality (HR 0·91; 95 % CI: 0·77, 1·08) or CVD-related mortality (HR 0·91; 95 % CI 0·70, 1·18) were observed. In conclusion, users of supplements generally lead healthier lifestyles than non-users and supplements did not confer any added advantage or harm relative to mortality risk. However, the intake of vitamin B6 and Zn from dietary supplements exceeded the recommended daily intake for almost a quarter of the supplement users.

FFQ are widely used in large-scale studies to assess dietary intake. To aid interpretation of diet–disease associations assessment of validity must be performed. Reproducibility is one aspect of validity focusing on the stability of repeated assessment with the same method which may also reveal problems in instrument design or participant instructions. The aim of the present study was to evaluate the reproducibility of a web-based FFQ targeting Danish adolescents within the Danish National Birth Cohort (DNBC). Data for the present study were obtained from a prospective design nested within the DNBC. Adolescents aged 13 to 15 years old (n 48, 60 % girls) completed the FFQ twice 4 weeks apart. The proportion of adolescents consistently classified into the same tertile according to amount of food intake ranged from 45 % (fish) to 77 % (vegetables), whereas classification into opposite tertiles ranged from 0 % (fruit, oils and dressing) to 15 % (beverages). Overall, no significant differences were observed in intake of food groups or nutrients between the two completions of the FFQ. Mean crude Spearman correlation for all food groups was 0·56 and mean intra-class correlation for all food groups was 0·61. In conclusion, the reproducibility of the FFQ for Danish adolescents was acceptable. The study revealed that adolescents aged 13–15 years seemed capable of recalling consistently overall dietary habits and had some difficulties estimating the frequency of consumption of regularly consumed food items.

Low vitamin D status may be associated with depression. Few studies have examined vitamin D and depression in older adults living at northern latitudes. The present study cross-sectionally investigated serum 25-hydroxyvitamin D (25(OH)D) status and depression among 5006 community-dwelling older persons (66–96 years) living in Iceland (latitudes 64–66°N). Depressive symptoms were measured by the fifteen-item Geriatric Depression Scale (GDS-15). Current major depressive disorder was assessed according to Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) criteria. Serum 25(OH)D was analysed using chemiluminescence immunoassay and categorised into three groups: deficient (<30 nmol/l); inadequate (30–49·9 nmol/l); and adequate (≥50 nmol/l). There were twenty-eight (2 %) men and fifty (1 %) women with current major depressive disorder. Mean GDS-15 scores for men and women with adequate vitamin D concentrations were 2·1 and 2·2, respectively. Men and women with deficient v. adequate vitamin D status had more depressive symptoms (higher GDS-15 scores) (difference 0·7 (95 % CI 0·4, 0·9) and 0·4 (95 % CI 0·1, 0·6), respectively). Furthermore, men with deficient vitamin D status were more likely to have current major depressive disorder (adjusted OR 2·51; 95 % CI 1·03, 6·13) compared with men with adequate vitamin D status. Associations among women were not significant. In this older population living at northern latitudes, deficient vitamin D status may be associated with depression. Further investigations are warranted to evaluate the pathways that may be associated with risk of depression among older adults.

Cod liver oil is a traditional source of vitamin D in Iceland, and regular intake is recommended partly for the sake of bone health. However, the association between lifelong consumption of cod liver oil and bone mineral density (BMD) in old age is unclear. The present study attempted to assess the associations between intake of cod liver oil in adolescence, midlife, and old age, and hip BMD in old age, as well as associations between cod liver oil intake in old age and serum 25-hydroxyvitamin D (25(OH)D) concentration. Participants of the Age, Gene/Environment Susceptibility–Reykjavik Study (age 66–96 years; n 4798), reported retrospectively cod liver oil intake during adolescence and midlife, as well as the one now in old age, using a validated FFQ. BMD of femoral neck and trochanteric region was measured by volumetric quantitative computed tomography, and serum 25(OH)D concentration was measured by means of a direct, competitive chemiluminescence immunoassay. Associations were assessed using linear regression models. No significant association was seen between retrospective cod liver oil intake and hip BMD in old age. Current intake of aged men was also not associated with hip BMD, while aged women with daily intakes had z-scores on average 0·1 higher, compared with those with an intake of < once/week. Although significant, this difference is small, and its clinical relevance is questionable. Intake of aged participants was positively associated with serum 25(OH)D: individuals with intakes of < once/week, one to six time(s)/week and daily intake had concentrations of approximately 40, 50 and 60 nmol/l respectively (P for trend < 0·001).

Fat-soluble vitamins A, E and K have been shown to play roles in immunity and inflammation, but studies on child allergic disease have been few and inconsistent. The aim of the present study was to examine the relationship between maternal intake of vitamins A, E and K in mid-pregnancy and child asthma and allergic rhinitis. We used data on 44 594 mother–child pairs from the Danish National Birth Cohort. Maternal intake of fat-soluble vitamins was calculated based on the information from a validated FFQ completed in mid-pregnancy. At 18 months, interviews with the mothers were conducted to evaluate doctor-diagnosed child asthma. At age 7 years, we assessed child asthma and allergic rhinitis using questions from the International Study of Asthma and Allergies in Childhood questionnaire and by national registries on hospital contacts and medication use. Current asthma was defined as asthma diagnosis and wheeze in the past 12 months by maternal report. We calculated multivariable risk ratios and 95 % CI by comparing the highest v. lowest quintile (Q) of maternal vitamin A, E and K intake in relation to child allergic disease outcomes. Maternal total vitamin K intake was directly associated with ever admitted asthma (Q5 v. Q1: 1·23, 95 % CI 1·01, 1·50) and current asthma at 7 years (Q5 v. Q1: 1·30, 95 % CI 0·99, 1·70). Weak inverse associations were present for maternal vitamin A and E intake during pregnancy with child allergic rhinitis. Maternal vitamin K intake during pregnancy may increase the risk of child asthma, and should be explored further on a mechanistic level. Conversely, maternal vitamin A and E intake may protect against child allergic rhinitis.

Dietary glycaemic index and glycaemic load (GL) have been related to obesity and other health outcomes. The objective of the present study was to examine the associations between maternal dietary GL and gestational weight gain, birth weight, the risk of giving birth to a child large-for-gestational age (LGA) or small-for-gestational age and postpartum weight retention (PPWR). Data were derived from the Danish National Birth Cohort (1996–2002), including data on gestational and lifestyle factors in pregnancy and 18 months postpartum. Dietary data were collected using a validated FFQ. Information on birth outcome was obtained through registers. A total of 47 003 women were included. The associations between the GL and birth outcome, gestational weight gain, assessed between weeks 12 and 30 of gestation, and PPWR were analysed by linear and logistic regression. Birth weight increased by 36 g from the lowest to highest GL quintile (95 % CI 19, 53 g), and an increased risk of LGA of 14 % was detected in the highest GL quintile compared with the lowest GL quintile. Among normal-weight and overweight women, higher gestational weight gain rates were detected in the highest GL quintile (26 g/week (95 % CI 19, 34) and 30 g/week (95 % CI 13, 46), respectively). The association between the GL and PPWR was most pronounced among pre-pregnant obese women, with an increase in weight retention of 1·3 (95 % CI 0·2, 2·8) kg from the lowest to highest GL quintile. The GL may play a role for excessive gestational weight gain and PPWR, which may be more pronounced among overweight and obese women.

Dairy products are important sources of micronutrients, fatty acids and probiotics which could modify the risk of child asthma and allergy development. To examine the association of dairy product intake during pregnancy with child asthma and allergic rhinitis at 18 months and 7 years in the Danish National Birth Cohort, data on milk and yoghurt consumption were collected in mid-pregnancy (25th week of gestation) using a validated FFQ (n 61 909). At 18 months, we evaluated asthma and wheeze using interview data. We assessed asthma and allergic rhinitis using a questionnaire at the age of 7 years and through registry linkages. Current asthma was defined as self-reported ever asthma diagnosis and wheeze in the past 12 months. All associations were evaluated using multivariate logistic regression. At 18 months whole milk was inversely associated with child asthma (≥5·5 times/week v. none: 0·85, 95 % CI 0·75, 0·97); the reverse was true for semi-skimmed milk (≥5·5 times/week v. none: 1·08, 95 % CI 1·02, 1·15). For yoghurt, children of women who ate low-fat yoghurt >1 serving/d had 1·21 (95 % CI 1·02, 1·42) greater odds of a medication-related ever asthma diagnosis compared with children of women reporting no intake. They were also more likely to have a registry-based ever diagnosis and report allergic rhinitis. Low-fat yoghurt intake was directly related to increased risk of both child asthma and allergic rhinitis, while whole milk appeared protective for early-life outcomes only. Nutrient components or additives specific to low-fat yoghurt may be mediating the increase in risk.