The consumption of various foods is internationally recommended in healthy diet although the association between dietary variety and incident dementia is unknown. We aimed to examine the association between dietary variety and the incidence of disabling dementia in older Japanese adults.

We conducted a prospective cohort study. Dietary variety was assessed based on the Dietary Variety Score (DVS). DVS was assessed by counting the number of ten food components (meat, fish/shellfish, eggs, milk, soyabean products, green/yellow vegetables, potatoes, fruit, seaweed and fats/oils) that were consumed almost daily using a FFQ. Participants were categorised into low (0–2 points), middle (3–4 points) and high (5–10 points) groups based on the DVS. Data on newly diagnosed disabling dementia were retrieved from the public long-term care insurance database. Cox proportional hazards regression was used to estimate hazard ratios (HR) with 95 % CI.

Yabu cohort study, Japan.

A total of 4972 community-dwelling adults aged 65 years or older.

During the median follow-up of 6·8 years, 884 participants were newly diagnosed with disabling dementia. After adjusting for confounders, the multivariable-adjusted HR for incident disabling dementia was 0·82 (95 % CI, 0·69, 0·97) for participants in the highest DVS category compared with those in the lowest DVS category (Pfor trend = 0·019).

A higher dietary variety is associated with a reduced risk of disabling dementia in older Japanese adults. These results have potential implications for the development of effective public nutritional approaches to prevent dementia in older adults.

Dietary questionnaires for assessing dietary intakes among populations of individuals aged 80 years or older (the very old) are very limited. We examined the relative validity of forty-three nutrients and twenty-seven food groups estimated by a brief-type self-administered diet history questionnaire (BDHQ) targeting very old Japanese, using semi-weighed dietary records (DR) as a reference.

Between June and August 2012 and between June 2015 and February 2016, a three-day non-consecutive DR (at two-week intervals) and a BDHQ were completed.

Tokyo, the capital prefecture of Japan.

Eighty very old Japanese (thirty-six men and forty-four women) aged 82–94 years.

The median intakes of 40–70 % of the crude and energy-adjusted nutrients estimated by the BDHQ were significantly different from those estimated by the DR. The median Spearman’s correlation coefficient of nutrient intakes between the BDHQ and the DR was 0·39–0·46. About half (48–56 %) of the food groups were significantly different in terms of the median intakes estimated by the BDHQ and the DR in crude and energy-adjusted values. The median Spearman’s correlation coefficient between the BDHQ and the DR was 0·45–0·48.

Acceptable Spearman’s correlations (≥0·3) were obtained for many dietary intakes among the very old Japanese population. The BDHQ is a good candidate for epidemiological studies among very old Japanese, although, for some nutrients and food groups, the difficulty of estimating accurate median intakes is one of the limitations for the tool. Further efforts to enhance the validity of the BDHQ for very old populations are needed.