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. Dietary antioxidant intake, especially in women, seems to modify the elevated death rate associated with high milk consumption.
Generated Summary
This research, a cohort study, investigated the association between milk, fruit, vegetable, and total antioxidant intakes and mortality rates in women and men. The study utilized data from the Swedish Mammography Cohort (SMC) and the Cohort of Swedish Men. The SMC provided data from 61,420 women (with 22,391 deaths) and a subsequent survey of 36,714 women. The Cohort of Swedish Men contributed data from 45,280 men (with 15,478 deaths). The primary aim was to determine whether higher mortality rates associated with high milk consumption are modified by fruit and vegetable intake or total antioxidant intake. The study used food frequency questionnaires to gather dietary information, and Cox regression with restricted cubic splines was employed for statistical analysis. The researchers aimed to identify whether the associations between milk consumption and mortality could be influenced by dietary factors such as fruit and vegetable intake or total antioxidant intake.
Key Findings & Statistics
- In women, consuming ≥3 glasses of milk per day and <1 serving/day of fruit/vegetables was associated with an adjusted hazard ratio for death of 2.79 (95% CI: 2.42, 3.21).
- Women consuming the same amount of milk but ≥5 servings/day of fruits/vegetables had a hazard ratio of 1.60 (95% CI: 1.40, 1.82).
- In men, the hazard ratios for the same comparisons were 1.31 (95% CI: 1.14, 1.51) and 1.07 (95% CI: 0.97, 1.18), respectively.
- Approximately 9% of the women reported milk consumption of ≥3 glasses/day in 1987–1990 (Table 1), whereas in 1997 only 2% reported such intake (Table 2).
- Men had on average higher consumption of milk; 15% drank ≥3 glasses/day in 1997 (Table 3).
- Average reported consumption of fruits and vegetables among women was 3.5 servings/day (standard deviation (SD), 2.0) at baseline and 5.3 servings/day (SD, 3.0) at the follow-up examination.
- Men reported an average consumption of 4.1 servings/day (SD, 2.5).
- During a mean follow-up period of 23 years (maximum 29 years), 22,391 women (total time at risk = 1,434,171 person-years) died.
- From January 1, 1998, onward, 10,314 women (581,785 person-years) and 15,478 men (687,688 person-years) died during a mean follow-up period of 15 years (maximum 17 years).
- Death rates increased in both sexes with increasing milk consumption (Figure 1A), and death rates decreased with higher consumption of fruit and vegetables (Figure 1B), as well as with higher ORACs (Figure 1C), although a threshold seemed to be discerned (>5 servings of fruit/vegetables per day and 15,000 µmol ORAC/day).
- In men, higher death rates started to be observed after only 3 or more glasses of milk per day (Figure 1A).
- In women, death rates were already increased at 1-2 glasses of milk per day.
- 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.
- In contrast, 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.
- In time-updated analysis of the SMC, a high intake of milk (≥3 glasses/day) with a concomitant low intake of fruit and vegetables (<1 serving/day) conferred a multivariable-adjusted hazard ratio of 2.79 (95% confidence interval (CI): 2.42, 3.21), and with a combined high intake of fruit and vegetables, the hazard ratio was 1.60 (95% CI: 1.40, 1.82).
- 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.
- If we used ORAC intake instead of fruit and vegetable intake as the effect-measure modifier, the estimates remained essentially unaltered.
- 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.
Other Important Findings
- The pattern was clearer with time-updated information as compared with a single exposure assessment.
- High milk consumption might shorten life span through increased oxidative stress.
- High milk consumption has long been promoted as strengthening bone and reducing the likelihood of fragility fractures.
- Oxidative stress and inflammation can be reduced by a diet rich in antioxidants (12–15), and such foods could potentially reduce rates of death (16, 17).
- High intake of fruits and vegetables or a high total antioxidant intake may counteract the observed associations of milk intake with mortality.
Limitations Noted in the Document
- The observational nature of the study limits the ability to establish causality.
- The study’s findings might not apply to populations with different ethnic backgrounds, especially those with a high prevalence of lactose intolerance.
- The study design does not allow for examining children and adolescents.
Conclusion
The study’s findings suggest that high milk consumption, particularly in women, may be associated with increased mortality rates, which is partially offset by the consumption of fruits and vegetables. The study highlights the importance of considering dietary patterns rather than focusing on single food items like milk. The authors emphasize the need for caution in recommending high milk consumption, especially for women not meeting fruit and vegetable intake recommendations. The observed interaction between milk intake and fruit and vegetable consumption in women underscores the complexity of dietary effects on health. These findings align with previous research suggesting that diets rich in antioxidants, found in fruits and vegetables, can mitigate the adverse effects of oxidative stress, a mechanism potentially linked to the impact of milk consumption. The study also suggests that the potential adverse effects of high milk consumption might be related to its lactose content and the subsequent production of galactose, which can induce oxidative stress. The study highlights that the association between milk consumption and mortality was more pronounced in women, suggesting potential sex-specific differences in the metabolism of milk components or the protective effects of other dietary factors. The findings provide insights into the complex interplay between diet, oxidative stress, and mortality. The authors suggest a potential mechanism by which milk consumption could affect mortality, related to the lactose content and subsequent oxidative stress. The authors suggest that the findings should be evaluated cautiously, and that further research should consider the influence of dietary patterns and genetic factors, specifically in the metabolism of milk and fruit and vegetables.
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