Prospective Cohort Study

B - Click here for explanation of classification scheme.

NEUTRAL: See Quality Criteria Checklist below.

To investigate long-term longitudinal associations of diet with glucose tolerance in elderly men included in the Finnish and Dutch cohorts of the Seven Countries Study.

• Finland cohort: All men born between 1900 and 1919 who were alive in 1959 and living in Ilomantsi, East Finland (N=832) and Poyta/Mellila, West Finland (N=888)
  
  • Of these men, 1,260 total men participated in a clinical examination and a dietary survey in 1969
  • In 1989 (30-year follow-up), 524 men were still alive
  • However, 470 (90%) men were examined and a random sample of 229 of these men participated in the dietary survey.
• Dutch cohort: In the town of Zutphen (eastern Netherlands)
  • In 1960, 878 men were examined for the first time
  • In 1970, 590 who followed-up at a 10-year examination and diet survey
  • In 1990, 314 men who were alive had a 30-year follow-up examination, with 238 (77%) of them taking part in the diet survey.

• Men known to have diabetes at the 30-year follow-up survey (N=46)
• Individuals who did not have complete data on diet and body mass index (BMI) from both the 10- and 30-year follow-up surveys and on glucose tolerance at the 30-year examination.

Recruitment

• Finland recruited men who were born between 1900 and 1919 in two communities: Ilomantsi and Poytya/Mellila
• The Dutch recruited men in one community: Zutphen.

Design

Cohort study: Men in the Finland and Dutch cohorts followed the following protocol

• All men were examined according to the protocol used in the Seven Countries Study
  • Clinical exams were performed by physicians specifically trained for the study
  • Height, weight and BMI were measured and calculated according to standard procedures
  • Standardized questions on the history of diabetes were asked
  • Food and beverage consumption data were collected by the cross-check dietary history method, which was used in both 1969-1970 and 1989-1990
  • Diet interviews were conducted by trained dietitians or nutritionists.
• At the 10-year follow-up survey in 1969-1970, information was also obtained about the habitual food consumption pattern during six to 12 months prior to the interview
• At the 30-year follow-up survery, the cross-check method was used, however foods were modified for age and different food availability
• At the 30-year follow-up, a standardized procedure for an oral glucose tolerance test (OGTT) was conducted according to the World Health Organization guidelines.

Statistical Analysis

• Descriptive statistics were used to describe the data
• A multiple regression analysis was used to investigate the association between diet and two-hour post-load glucose
• Adjustments were made for age, past BMI, past energy intake, seasonal variation and other potential confounders
• Regression analyses were used on several nutrients
• Only pooled results were presented because no interaction concerning diet and glucose tolerance was noted between and within the two cohorts
• P-values were based on two-sided tests of statistical significance.

Timing of Measurements

• 1959-1960: Baseline
• 1969-1970: 10-year follow-up
• 1989-1990: 30-year follow-up.

Dependent Variables

Glucose tolerance was measured through a two-hour glucose tolerance test.

Independent Variables

Dietary habits: Information on habitual food consumption was obtained using the cross-check dietary history method.

Control Variables

• Cohort
• Age
• Past BMI
• Past intake of energy
• Past consumption of foods.

Initial N   

• Finland cohort: 490 (90%) of 524 alive men were exaimined and 229 men took the diet survey at the 30-year follow-up in 1989-1990
• Dutch cohort: 238 (77%) of 314 alive men were surveyed and examined at the 30-year follow-up in 1989-1990.

Attrition (Final N)

• Complete data from 338 Finnish and Dutch men was used in the study
• 46 men were excluded at the 30-year follow-up, due to known diabetes.

Age

1989-1990

• Finland cohort was between 70-89 years of age
• Dutch cohort age was 76.0±0.4 years.

Ethnicity

Finland and Dutch.

Other Relevant Demographics

No.

Anthropometrics

Cohorts were similar in BMI with a range of 25.5 to 26.8 in 1989-1990.

Location

• Ilomantsi, Poytya and Mellila, Finland
• Zutphen, Netherlands.

Past Dietary Characteristics (1969-1970) and Changes in Intake During the 20-Year Follow-Up, Explaining Two-Hour Plasma Glucose (1989-1990) in Multiple Regression Analyses Among 338 Participants of the Finnish and Dutch Cohorts of the Seven Countries Study

Nutrient	Beta	SE	Beta	SE
Protein (Percentage of Energy)	-0.177	0.096	-0.121	0.058*
Fat (Percentage of Energy)	0.083	0.033*	0.031	0.023
Saturated Fat	0.108	0.047*	0.030	0.034
Vitamin C (mg/1,000kcal)	-0.028	0.012*	-0.005	0.006

Nutrient data was adjusted for cohort, age, past BMI and past energy intake
*P<0.05.

Other Findings

• The highest mean two-hour glucose level was seen in West Finland men
• The highest proportion of protein to kcal and the lowest proportion of fat to kcal was found in the diet of East Finland men
• West Finland men had the lowest energy-adjusted intake of dietary fiber and the highest energy-adjusted intake of dietary cholesterol
• The energy-adjusted intake of alcohol and vitamin C was the highest in the Dutch cohort and they had the lowest proportion of saturated fat to kcal
• The prevalence of of newly-diagnosed diabetes among all men was 8%. 21% of the men had impaired glucose tolerance (IGT).
• Men with no IGT had a lower BMI, compared to men with IGT and newly-diagnosed diabetes
• Men with IGT had a lower proportion of protein and a higher proportion of mono- and di-saccharides in their diet, compared to men with no IGT 
• Men with new diagnosed diabetes had the highest intake of fat
• Changes in the consumption of foods was observed over the 20 years, with an increase in the relative consumption of fruit, berries, cereals, milk products and fish, which almost doubled, whereas potato consumption decreased
• An increase in fish, potato, vegetable and legume consumption during the 20-year follow-up was associated with a reduced two-hour plasma glucose level, after adjustment for cohort, age, past BMI, past intake of energy and the past consumption of these foods (P<0.05)
• Adjusting for age and cohort, the intake of total, saturated and monounsaturated fatty acids and dietary cholesterol 20 years before diagnosis was higher in men with newly-diagnosed diabetes in the survey than in men with normal or impaired glucose tolerance
• After adjustment for cohort, age, past BMI and past energy intake, the past intake of total fat was positively associated with two-hour post-load glucose level (P<0.05)
• An independent inverse association with the past intake of vitamin C was observed (P<0.05)
• These associations were independent of changes in the intake of fat and vitamin C during the 20-year follow-up.

• The authors suggest that the intake of fat (especially saturated fat) is associated with the development of IGT and diabetes, independent of confounding factors such as age, BMI and energy intake
• The authors also suggest that vitamin C is associated with a reduced development of IGT and diabetes.

Not-for-profit

National Institute on Aging, National Institutes of Health, the Prevention Foundation, the Netherlands; Medical Research Council and Research Council for Agriculture and Forestry, Academy of Finland;and the Sandoz Gerontological Foundation.

• Insufficient information was provided on how the participants were recruited into the cohorts
• Other health factors that may have affected the study population were not discussed or excluded, i.e., heart disease
• More demographic and health information would have been helpful to determine the comparability between the cohort groups at the 30-year follow-up.
• The reasons for withdrawals were unclear within the cohort groups. Not all of the participants were accounted for in the cohorts at the 30-year follow-up, when the data was combined.