Subjects and data collection
The data used in this study were obtained from the samples from two studies: the National Swedish Food Survey of Adults (Riksmaten Adults) and the Malmö Diet and Cancer Study (MDCS). Riksmaten Adults is the most recent national dietary survey in Sweden , while the MDCS, although more dated and locally collected, has one of the highest-quality dietary data in the country [20, 21]. The combined data from these two studies provide information on dietary consumption for over 20 years.
In the Riksmaten Adults survey, participants were between 18 and 80 years old and resided in Sweden. The data collection process took place between May 2010 and July 2011. Based on information from the National Registry of Statistics Sweden, 5000 invitations were sent to potential participants with the intent of recruiting a representative sample of the Swedish population (in regard to gender, age group, and region). The participants completed a web-based 4-day food diary (see below) and answered a questionnaire that included questions on height and weight, as well as lifestyle and socioeconomic factors. The questionnaire was answered online, but an interviewer assisted (by telephone) those participants who could not access the website. All participants recruited for Riksmaten Adults gave oral informed consent after they received information about the study and the voluntary nature of their participation and before any measurements were performed. In total, 2268 individuals participated in Riksmaten Adults, and of the participants, 1797 (44% males) completed the food diary (36% participation rate; 31% for men and 40% for women) .
The MDCS is a population-based prospective cohort study in which all men born between 1923 and 1945 and women born between 1923 and 1950 who resided in Malmö (in the south of Sweden) during the data collection period (March 1991 – October 1996) were invited via a personal letter or advertisement to participate in the MDCS (n = 74,138) . Only those with limited knowledge of Swedish or mental incapacity were excluded from participation . The data collection included a dietary assessment (see below), a self-administered lifestyle and socioeconomic questionnaire, and anthropometric measurements (including height and weight). A total of 28,098 participants, of which 39% were men, were included in the study after completing the baseline survey. The participation rate was 41% (38% for men and 43% for women) . In September 1994, the routine for coding dietary data was slightly altered to shorten the dietary interview from 60 to 45 min . The energy intake was slightly lower after the change, and because we are investigating absolute intakes of micronutrients, we included only those individuals who completed the longer, and therefore more detailed, dietary interview (n = 15,107). In addition, we excluded participants who were considered to have reported an inadequate energy intake (n = 2869). Those energy misreporters were identified by comparing the reported energy intake with the estimated energy expenditure . Thus, the final sample used in the present study included 12,238 individuals (45% men). The Ethical Committee at Lund University approved the MDCS (LU 51–90), and all the participants provided written informed consent.
Dietary data collection
For the Riksmaten Adults survey, a web-based 4-day food diary was used to record everything that the participants had eaten or drunk during the whole day, day-by-day and meal-by-meal, as well as the time and place at which the meal was consumed. The website was linked to the national food composition database containing more than 1900 food items. If foods were missing from the survey, the participants were asked to choose the closest alternative or to register the different ingredients separately. The web tool also offered the possibility to register the method of preparation (raw, boiled, fried, etc.) to adjust for the loss of certain nutrients based on cooking methods. To cover the variation in the dietary pattern within the week, the 4-day food diary was randomly selected to start on different days of the week; the selection was divided into four rounds performed quarterly to cover seasonal variation. All the subjects who decided to take part in the study received a portion guide booklet (with pictures to help the participants estimate the portion size of the servings), a notebook (to describe the foods consumed in as much detail as possible, as well as the intake of supplements), and an information folder explaining how to register the food and navigate the food diary website. The average daily food intake was estimated based on the information from the 4-day food diary. Nutrient intake, including the intakes of monosaccharides and disaccharides (including sucrose separately), was calculated using the national food composition database .
For the MDCS, the dietary data were collected using a combination of three methods. First, a 7-day food diary was used to record prepared meals (lunch and dinner mostly), as well as cold drinks, and/or supplements with the intention of collecting information concerning the current diet. Second, a food frequency questionnaire was used to record the consumption frequency and portion size of 168 items that are eaten regularly and that were not covered by the food diary (covering mostly breakfast, snacks and hot drinks); portion sizes were estimated by the participants using a booklet containing pictures with 4 different portion sizes of up to 48 food items. And third, a 60-min interview with trained personnel was conducted to complete the survey; in this interview, the participants could share details regarding the method of preparation and portion sizes of the items recorded in the food diary with a trained interviewer. During the interview, the staff also checked that there was no overlap from the two sources of dietary information. The collected data were then introduced into a software program to compare the data with those from the Malmö Food and Nutrient Database, which was based on the Swedish Food Database PC KOST-93 [24, 26, 27]. The details of the MDCS data collection process [22, 23, 28] and the validity of the methods used [20, 21] are described elsewhere.
Added sugar variable
Added sugar intake was estimated for each individual by totaling the intake of monosaccharides (mainly glucose and fructose) and sucrose from the whole diet and then subtracting the amount of monosaccharides and sucrose from fruits and berries, fruit juice, and vegetables (i.e., the main sources of naturally occurring sugars) . The percentages of nonalcoholic energy intake (%E) for added sugar were calculated, and the populations were stratified into six groups according to their added sugar intake as follows: less than 5%E, 5–7.5%E, 7.5–10%E, 10–15%E, 15–20%E, and greater than 20%E from added sugar. These cut-off points were selected with the intention of comparing our results with already existing added sugar intake recommendations.
Other dietary variables
The selection of micronutrients was performed based on the available information in the datasets, the concern expressed by the Nordic Nutrition Recommendations (NNR) regarding possible low levels in the population, and the involvement of the micronutrients in the prevention or development of lifestyle-related diseases , as well as their presence in previous studies on micronutrient dilution [9,10,11,12,13,14,15,16,17,18]. Ultimately, nine micronutrients were included: calcium (mg/day), folate (μg/day), iron (mg/day), magnesium (mg/day), potassium (mg/day), selenium (μg/day), vitamin C (mg/day), vitamin D (μg/day), and zinc (mg/day). The dietary composition in terms of carbohydrates, fat, protein, and fiber was calculated as the percentage of nonalcoholic energy intake.
All statistical analyses were performed in the two populations separately using SPSS version 24 (IBM Statistics; New York, USA). Statistical significance was indicated by p < 0.05. Age and body mass index (BMI; calculated using height (m) and weight (kg), expressed as kg/m2) were analyzed for the whole sample and across the added sugar categories using an ANOVA test.
The mean daily intake and 95% confidence intervals (CIs) of the selected micronutrients and the macronutrients (as %E) were calculated for each group of added sugar intake using a general linear model adjusted for age, sex, BMI and energy intake. We also examined whether there was a linear association by using the added sugar groups as a continuous variable in the model. In addition, the number and percentage of participants with intakes below the dietary reference values (DRVs), i.e., the average requirement (AR) and recommended intake (RI) specific for the Nordic countries, as per the NNR 2012, were calculated. A chi-square test was performed to investigate whether the distribution differed between the observed and expected values. AR was defined as the nutrient level that is sufficient to cover the requirement of half of the population in a certain age and gender group, and RI is the nutrient level that meets the known requirement among almost all healthy individuals . Since the DRVs are often different for men and women, sex-specific values were obtained. Recommendations for iron differ for women based on age and menopausal status. Therefore, the premenopausal threshold of iron was chosen for the female participants in Riksmaten Adults, and the postmenopausal cut-off was used for the females in the MDCS. The folate RI thresholds used for both populations were those established for individuals aged 31 and older, and the RI for vitamin D used for both populations was the value for individuals up to 74 years old.