Abstract and Introduction
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.
High milk consumption has long been promoted as strengthening bone and reducing the likelihood of fragility fractures. However, we recently demonstrated a higher risk of fracture with high daily milk consumption in women. Mortality rates were also increased in both women and men with high milk consumption. We hypothesized that the underlying mechanism could be explained by the lactose content of milk.
Milk is the main dietary source of d-galactose, one component of the disaccharide lactose. Chronic d-galactose exposure in animals, with a dose corresponding to 1–2 glasses of milk in humans,[1,2] is deleterious to health by means of oxidative stress damage and chronic inflammation.[2–5] Female animals seem to be especially vulnerable.[6–8] The increased oxidative stress with aging and chronic low-grade inflammation is not only a pathogenic mechanism of cardiovascular disease and cancer in humans[9,10] but also a mechanism of age-related bone loss and sarcopenia.[10,11]
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] Because of the antioxidant capacity of vegetables and fruits and the high content of lactose/galactose in milk, which may induce oxidative stress and low-grade inflammation, we hypothesized that a high intake of fruits and vegetables or a high total antioxidant intake[18,19] may counteract the observed associations of milk intake with mortality. Indeed, experimental evidence in animals indicates that galactose-induced aging can be prevented by a higher intake of fruits and vegetables.[20–24]
To our knowledge, no previous clinical study has combined milk consumption with fruit and vegetable intake and total antioxidant intake to evaluate associations with the rate of death. In Scandinavia, consumption of milk and of fruits and vegetables displays a wide range in intake.[1,25,26] Therefore, our main objective in this Swedish cohort study was to determine whether fruit and vegetable intake or total antioxidant intake modifies the previously observed relationship between milk consumption and death.
Am J Epidemiol. 2017;185(5):345-361. © 2017 Oxford University Press