Milk Fat Intake and Telomere Length in U.S. Women and Men: The Role of the Milk Fat Fraction

You'll need your doctor to analyze these 8 posts on dairy fat because they mostly come to the opposite conclusion about health benefits. I'm doing full fat milk, it tastes better. Did skim milk for decades prior to stroke.

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Milk Fat Intake and Telomere Length in U.S. Women and Men: The Role of the Milk Fat Fraction

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Larry A. Tucker¹

¹Brigham Young University, College of Life Sciences, 106 SFH, Provo, Utah 84602, USA

Academic Editor: Ana Lloret

Received06 Jun 2019

Accepted04 Oct 2019

Published28 Oct 2019

Abstract

The associations between milk intake frequency and milk fat consumption and telomere length, an index of biological aging, were studied using an NHANES sample of 5,834 U.S. adults and a cross-sectional design. The milk consumption variables were assessed with the NHANES Diet Behavior and Nutrition questionnaire. The quantitative polymerase chain reaction method was used to measure leukocyte telomere length. Results showed that milk consumption frequency was not related to telomere length; however, there was a strong association between milk fat intake and telomere length. With the sample delimited to milk drinkers only, milk fat intake was linearly and inversely related to telomere length, after adjusting for the covariates (F=8.6,P=0.0066). For each 1 percentage point increase in milk fat consumed (e.g., 1% to 2%), adults had more than 4 years of additional biological aging. With milk fat intake divided into 5 categories (i.e., milk abstainers, nonfat, 1%, 2%, and full-fat milk), mean telomere lengths differed across the categories (F=4.1,P=0.0093  ). The mean telomere difference between the extremes of milk fat intake (nonfat vs. full-fat) was 145 base pairs, representing years of additional biological aging for full-fat milk consumers. Effect modification testing indicated that the milk fat and cellular aging association may be partly due to saturated fat intake differences across the milk fat groups. When the sample was delimited to adults reporting only high total saturated fat intake (tertile 3), the milk fat and telomere relationship was strong. However, when the sample was restricted to adults reporting only low saturated fat consumption (tertile 1), there was no relationship between milk fat intake and telomere length. Overall, the findings highlight an association of increased biological aging in U.S. adults who consumed high-fat milk. The results support the latest Dietary Guidelines for Americans (2015–2020), which recommend consumption of low-fat milk, but not high-fat milk, as part of a healthy diet.

1. Introduction

Investigations evaluating the effect of adult milk consumption on health and disease have produced inconsistent findings. Some studies indicate that the consumption of cow’s milk promotes health, while others show that it increases risk of disease and mortality. Numerous investigations highlight the mixed results.
In a 2018 study by Feskanich et al. [1], milk intake was associated with a lower risk of hip fracture, whereas in a 2018 investigation by Michaelsson et al., milk consumption was linked to an increased risk of hip fracture [2]. Further, a meta-analysis that included six studies focusing on women and three of men concluded that milk intake and hip fracture are unrelated [3].
In a meta-analysis of 19 studies concentrating on colorectal cancer, Aune et al. [4] determined that milk intake reduces risk, whereas in an evaluation of 32 investigations, the same researcher [5] concluded that milk consumption increases risk of prostate cancer. Similarly, some research indicates that dairy intake reduces the risk of type II diabetes [6, 7], whereas other studies show that dairy consumption is linked to increased insulin resistance [8–10]. Several investigations have concluded that dairy intake is unrelated to type II diabetes and associated metabolic factors [11, 12]. Lastly, in a Japanese cohort, milk intake was inversely associated with all-cause mortality [13], but in a Swedish group, milk consumption was related to increased all-cause mortality [14].
Clearly, the effects of adult milk consumption on health and disease are varied, and in recent years, questions about the influence of milk have been further complicated with debate about the effect of milk fat on disease risk. Is low-fat milk a healthier choice than full-fat? According to a 2017 study by Tognon et al., all-cause mortality is significantly higher among adults who consumed full-fat milk compared to medium- or low-fat milk [15]. Similarly, Talaei et al. found that Iranians who drink whole milk daily are at higher risk of all-cause mortality than their counterparts [16]. Likewise, whole milk intake is predictive of elevated prostate cancer mortality in studies by Lu et al. [17] and Song et al. [18]. Conversely, according to Crichton and Alkerwi, high intake of whole-fat dairy is inversely associated with obesity and abdominal adiposity compared to those with low consumption [19]. Additionally, research by Drehmer et al. shows that full-fat, but not low-fat, dairy is favorably related to the metabolic syndrome in adults [20].
The effects of milk and milk fat on cancer, heart disease, diabetes, and all-cause mortality have been reviewed extensively in the literature. With some investigations showing positive outcomes and others revealing negative, there remains much to learn about the effect of cow’s milk on health and disease in adults. The influence of milk fat, particularly low-fat compared to full-fat, also needs clarification.
To date, the influence of milk and milk fat on inflammation, oxidative stress, and cellular longevity has received little attention. Cellular longevity is often indexed objectively by measuring the length of telomeres [21, 22]. Adults with short telomeres tend to have more oxidative stress and chronic disease, including more heart disease, depression, obesity, and cancer, as well as earlier death, than their counterparts [23–25].
Telomeres add stability to and help safeguard chromosomes. Telomeres cap the ends of chromosomes with nucleoproteins. A simple analogy is that telomeres function like the caps that protect the end of shoe laces. Over time, as cells divide, telomeres become progressively and predictably shorter.
Although chronological age is the key factor accounting for the length of telomeres, other things contribute significantly. Research shows that oxidative stress is a critical factor [26, 27]. Moreover, lifestyle plays a major role. For instance, people who smoke have shorter telomeres than nonsmokers [28]. Adults with obesity have shorter telomeres than their counterparts [29], and inactive individuals have shorter telomeres than those who are physically active [30].
Biological aging is also affected by diet. Regular intake of healthy foods like nuts and seeds is associated with longer telomeres [31], whereas consumption of less healthy foods, like processed meats, is related to shorter telomeres [32]. Fiber intake goes hand-in-hand with longer telomeres [33], as does higher vegetable intake [34] and regular fruit consumption [35]. However, consumption of fats and oils is associated with shorter telomeres and increased biological aging [36, 37].
From a more physiological and molecular nutrition perspective, milk is a postnatal endocrine signaling system [38]. Milk consumption encourages mTORC1-mediated anabolism and growth. For example, extended full-fat cow’s milk consumption in mice increases energy intake and body weight and reduces insulin signaling in white adipose tissue compared to low-fat milk intake [39]. According to Melnik, to accomplish its mTORC1-activating role, four metabolic messengers are provided by milk: “1. essential branched-chain amino acids, 2. glutamine, 3. palmitic acid, and 4. bioactive exosomal microRNAs…” [38].
Research by Yasuda et al. indicates that unsaturated and saturated fatty acids have opposite effects on podocyte apoptosis by controlling mTORC1 activity via translocation onto lysosomal membranes [40]. Insulin and IGF-1 and essential branched-chain amino acids influence mTORC1 by activation of the kinase AKT pathway. Palmitic acid, the primary saturated fatty acid of milk fat globules, also activates mTORC1 at the lysosome [40]. In short, it appears that repeated mTORC1 activation contributes to endoplasmic reticulum stress, leading to premature aging and disease [38].
Although much is understood about diet, oxidative stress, and cellular longevity, the role of cow’s milk consumption, particularly milk fat, remains unclear. To date, the relationship between milk fat intake and telomere length has rarely been studied. Hence, the present study was conducted. Its purpose was to determine the extent cow’s milk consumption and the fat content of the milk account for differences in cellular aging, indexed using leukocyte telomere length in 5,834 women and men, representative of the U.S. adult population. A secondary objective was to assess the extent demographic, lifestyle, and other dietary factors influence the milk and telomere relationships. The role of saturated fat intake, a major part of the fat content of cow’s milk, was also a significant focus of the investigation.