Abstract
High milk consumption might shorten life span through increased oxidative stress. We aimed to determine whether higher mortality rates with high milk consumption are modified by fruit and vegetable intake or total antioxidant intake (oxygen radical absorbance capacity). We used information from food frequency questionnaires completed by 61,420 women in a Swedish cohort (22,391 deaths from the 1987–1990 baseline onward), 36,714 women from a second survey (1997) of this cohort, and 45,280 Swedish men (15,478 deaths from the 1998 baseline onward). Compared with low consumption of milk (<1 glass/day) and high consumption of fruits/vegetables (≥5 servings/day), time-updated information revealed an adjusted hazard ratio for death of 2.79 (95% confidence interval (CI): 2.42, 3.21) in women who consumed ≥3 glasses of milk/day and <1 serving/day of fruit/vegetables and a hazard ratio of 1.60 (95% CI: 1.40, 1.82) in women who consumed the same amount of milk but ≥5 servings/day of fruits/vegetables. The same comparisons in men, based on a single food frequency questionnaire, displayed hazard ratios of 1.31 (95% CI: 1.14, 1.51) and 1.07 (95% CI: 0.97, 1.18), respectively. Total antioxidant consumption showed similar patterns as fruit/vegetable intakes.
Generated Summary
This study is a population-based cohort study that aimed to determine whether fruit and vegetable intake or total antioxidant intake modifies the previously observed relationship between milk consumption and death. The researchers used data from two previously described population-based cohort studies, the Swedish Mammography Cohort (SMC) and the Cohort of Swedish Men. The SMC started in 1987–1990, and the Cohort of Swedish Men was established in 1997. The study examined the associations of milk consumption with mortality rates, considering the modifying effects of fruit and vegetable intake and total antioxidant intake. The study focused on a wide range of milk intakes and antioxidant food intakes, with the primary outcome being all-cause mortality, and the secondary outcomes being mortality from cardiovascular diseases and cancer. Time-updated information was used to analyze the data, and the researchers utilized restricted cubic-spline Cox regression to evaluate trends in mortality rates.
Key Findings & Statistics
- In women who consumed ≥3 glasses of milk/day and <1 serving/day of fruit/vegetables, the adjusted hazard ratio for death was 2.79 (95% confidence interval (CI): 2.42, 3.21).
- In women who consumed the same amount of milk but ≥5 servings/day of fruits/vegetables, the hazard ratio was 1.60 (95% CI: 1.40, 1.82).
- In men, the hazard ratio was 1.31 (95% CI: 1.14, 1.51) for those consuming ≥3 glasses of milk/day and <1 serving/day of fruit/vegetables.
- The hazard ratio was 1.07 (95% CI: 0.97, 1.18) in men consuming ≥3 glasses of milk/day and ≥5 servings/day of fruits/vegetables.
- In the time-updated analysis of the Swedish Mammography Cohort (SMC), a high intake of milk (≥3 glasses/day) with a low intake of fruit and vegetables (<1 serving/day) conferred a multivariable-adjusted hazard ratio of 2.79 (95% CI: 2.42, 3.21).
- In women with a single exposure assessment, the corresponding estimates were 1.81 (95% CI: 1.03, 3.20) and 1.10 (95% CI: 0.88, 1.38), respectively.
- The same comparisons in men revealed a hazard ratio of 1.31 (95% CI: 1.14, 1.51) for high consumers of milk with a low fruit and vegetable intake and a hazard ratio of 1.07 (95% CI: 0.97, 1.18) for high consumers of milk who also consumed 5 or more servings of fruits and vegetables per day.
- In the Swedish Mammography Cohort (Women) in 1987-1990, approximately 9% of the women reported milk consumption of ≥3 glasses/day.
- In 1997, only 2% of women reported such intake.
- Men had a higher milk consumption, with 15% drinking ≥3 glasses/day in 1997.
- Average reported consumption of fruits and vegetables among women was 3.5 servings/day at baseline and 5.3 servings/day at follow-up.
- Men reported an average consumption of 4.1 servings/day.
- The rate of mortality was highest among persons consuming less than 1 serving of fruit and vegetables per day combined with high milk consumption.
- In the Swedish Mammography Cohort (Women) during 1987-1990 baseline and time-updated analyses, the mortality rate was 22.5 (95% CI: 20.3, 24.8) for those consuming <1 serving of fruit/vegetable and <1 milk intake.
- In the Cohort of Swedish Men, in 1997, the mortality rate was 32.8 (95% CI: 29.6, 36.3) for those consuming <1 serving of fruit/vegetable and <1 milk intake.
Other Important Findings
- High milk consumption was associated with increased mortality rates in both women and men.
- Higher consumption of fruits and vegetables, as well as higher ORACs, were associated with decreased mortality rates.
- The pattern of increased mortality with higher milk consumption was more clearly observed with time-updated information.
- The relative excess risk of interaction estimate of 0.37 (95% CI: 0.01, 1.27) in the time-updated analysis of women indicated a modest additive interaction.
- No significant interaction was discovered among men.
- Death rates increased in both sexes with increasing milk consumption, and death rates decreased with higher consumption of fruit and vegetables.
- In women, death rates were already increased at 1-2 glasses of milk per day.
- Associations with milk intake were further adjusted for intake of fruit and vegetables, and associations with fruit and vegetable intake and ORAC were adjusted for intake of milk.
Limitations Noted in the Document
- The study’s results might not apply to people of other ethnic origins, such as those with a high prevalence of lactose intolerance.
- The study results might not be applicable to children and adolescents.
- The study found no clear interaction between milk intake and fruit and vegetable intake in men, which could have been due to the more modest association between milk and mortality in men.
- There is a potential for measurement error in the dietary data due to the use of food frequency questionnaires.
- The study design is observational, and therefore, causal inferences should be made with caution.
- The study did not address the specific mechanisms through which milk consumption might affect mortality.
Conclusion
The observational findings in this study of Swedish adults raise questions about recommending high consumption of milk, especially in women who do not meet the recommended intake of fruits and vegetables. The study observed that mortality rates were highest in persons with high milk consumption combined with low consumption of fruits and vegetables or a low ORAC, while the lowest age-adjusted mortality rates were found in women and men who reported high consumption of fruits and vegetables or had high ORACs combined with low intake of milk. The association between milk and mortality was more pronounced in women, and an additive interaction for mortality rates between milk consumption and fruit and vegetable consumption was found only in women. Further research is needed to explore the potential mechanisms behind these associations and to determine whether these findings are generalizable to other populations. The study suggests that the recommendation for high milk consumption should be carefully considered, especially for women. The study underscores the importance of a diet rich in fruits and vegetables in reducing mortality risk. As stated in the study, “The rate of mortality was highest among persons consuming less than 1 serving of fruit and vegetables per day (or in the lowest quartile of ORAC) combined with a high consumption of milk, in both men and women.”
IFFS Team Summary
- study of over 140 000 men and women over years in Sweden
- Compared to sex matched subjects who consumed maximum one glass of milk per day, but 5 or more serving of fruits and vegetables
- Women consuming three or more glasses of milk , and one or less servings of vegetables had a mortality HR of 2.79
- Women consuming three or more glasses of milk , and five or more servings of vegetables had a mortality HR of 1.60
- In men, the same comparison yielded HR of 1.31 and 1.07 – the latter not been statistically significant
- possibly hard to find a distinction in men if overall animal protein consumption is high