Large Variability of Iodine Content in Retail Cow's Milk in the U.S

Cow milk is an important source of iodine for prenatal health, and switching to plant-based milk can lead to iodine insufficiencies

Iodine insufficiencies are common among many populations, particularly pregnant women. One of the main functions of iodine is making thyroid hormone. The 2 main hormones that iodine influences are triiodothyronine and thyroxine. Thyroid hormone affects metabolism of most tissues. For the average adult, the recommended dietary allowance (RDA) for iodine is 150 µg. During certain stages of life, such as pregnancy, lactation, and infancy, the importance of iodine is even greater as it supports brain, bone, and organ development. The RDA for iodine during pregnancy is 220 µg and, during breastfeeding, the RDA is 290 µg. Consuming enough iodine in the diet during pregnancy helps support fetal neurodevelopment. Iodine is found in several food sources such as seafood and iodized salt; however, dairy products are one of the major sources of iodine in American diets. It is important to note that only bovine milk products are rich in this mineral. One cup of milk provides 39% and 57% of the daily iodine needs for the average adult woman and pregnant woman, respectively. As the Dietary Guidelines for Americans (DGA) recommend limiting sodium intake, which includes iodized salt, dairy may be an especially important source of iodine. However, according to the USDA, about 90% of the US population does not meet the dairy recommendations presented in the DGA. In recent years, plant-based diets have received a lot of attention. A market for plant-based milk alternatives has grown and includes a variety of options such as almond, soy, and oat milk. Plant-based milks do not naturally contain iodine and are typically not fortified with iodine. Women of childbearing age who drink plant-based milks instead of cow milk have lower urinary iodine concentrations than women who consume cow milk. This review will focus on the importance of iodine in the diet to support prenatal health, lactation, and infant health.

Iodine Intake Trends in United States Girls and Women between 2011 and 2020

BACKGROUND

Usual intakes of iodine in United States girls and women, including pregnant and lactating women have not been adequately studied. Adequate intake of iodine is critical for neurodevelopment of girls, thyroid functions, and reproductive health of women.

OBJECTIVES

This study aimed to examine the adequacy and trends of iodine intake of United States girls and women between 2011 and 2020.

METHODS

We mapped the sources of United States girls and women's iodine intake from the 29 food groups between 2011 and 2020 using United States Department of Agriculture's iodine data release 2. The total food intakes from 2 d of dietary recall of the United States National Health and Nutritional Examination Survey and estimated iodine concentrations of the food groups were used to calculate the usual iodine intakes of female participants. Trends of usual intakes, urinary iodine concentrations (UIC), and estimated intake adequacy were calculated.

RESULTS

Median usual intakes of iodine estimated from diet and supplements and UIC of United States girls and nonpregnant, nonlactating women declined between 2011 and 2020 in all 3 age groups: ≤14 y, 15-49 y old, and ≥50 y. Median usual intakes of iodine for pregnant and lactating United States women declined as well. Inadequacy levels of usual iodine intake were 9.9% for nonpregnant, nonlactating women of reproductive age 15-49 y old, 40.3% for lactating, and 10.2% for pregnant women in the 2017-2020 period. Intake insufficiencies estimated from UIC were 48.8%, 63.2%, and 31.3% for nonpregnant, nonlactating women of reproductive age 15-49 y old, pregnant and lactating women, respectively, in the 2017-2020 period. A significant decline in milk consumption might be one of the major contributors to the dietary iodine decline in United States women.

CONCLUSIONS

Iodine intake of United States girls and women were on the decline between 2011 and 2020 and the increased inadequacy of iodine intake deserves public health attention.

Nutritional and health benefits and risks of plant-based substitute foods

Plant-based substitutes (PBS) are seen as a convenient way to transition to a more plant-based diet, but their potential health benefits and nutritional concerns remain debated. Based on a review of the literature, it is concluded here that the primary risk of insufficient nutrient intake with PBS concerns iron and calcium, which are critical to the nutritional value of PBS. Other risks were identified but these would depend on the characteristics of the overall diet, as is the case for iodine in a diet containing no seafood or dairy, and vitamin B12 in a vegetarian/vegan diet. Conversely, the use of PBS is also expected to confer some benefits for long-term health because it would result in higher fibre intakes (in the case of meat PBS) and lower SFA intakes (but higher PUFA/MUFA intakes), but attention should be paid to a potential increase in sodium intake with PBS of meat products. In fact, a recurring finding in this review was that PBS is a very heterogeneous food category involving considerable variations in ingredient and nutrient composition, and whose design could be improved in order to foster nutritional and health benefits. The latter also depend on the animal food that is being replaced and are only deemed likely when PBS replace red meat. The fortification of PBS with key nutrients such as iron and calcium may constitute an actionable public health solution to further shift the balance in favour of PBS in the context of the current dietary transition in western countries.

Effect of dietary seaweed (Ascophyllum nodosum) supplementation on milk mineral concentrations, transfer efficiency, and hematological parameters in lactating Holstein cows

This study investigated the effect of feeding seaweed (Ascophyllum nodosum) to dairy cows on milk mineral concentrations, feed-to-milk mineral transfer efficiencies, and hematological parameters. Lactating Holstein cows (n = 46) were allocated to 1 of 2 diets (n = 23 each): (1) control (CON; without seaweed) and (2) seaweed (SWD; replacing 330 g/d of dried corn meal in CON with 330 g/d dried A. nodosum). All cows were fed the CON diet for 4 wk before the experiment (adaptation period), and animals were then fed the experimental diets for 9 wk. Samples included sequential 3-wk composite feed samples, a composite milk sample on the last day of each week, and a blood sample at the end of the study. Data were statistically analyzed using a linear mixed effects model with diet, week, and their interaction as fixed factors; cow (nested within diet) as a random factor; and data collected on the last day of the adaptation period as covariates. Feeding SWD increased milk concentrations of Mg (+6.6 mg/kg), P (+56 mg/kg), and I (+1,720 μg/kg). It also reduced transfer efficiency of Ca, Mg, P, K, Mn, and Zn, and increased transfer efficiency of Mo. Feeding SWD marginally reduced milk protein concentrations, whereas there was no effect of SWD feeding on cows' hematological parameters. Feeding A. nodosum increased milk I concentrations, which can be beneficial when feed I concentration is limited or in demographics or populations with increased risk of I deficiency (e.g., female adolescents, pregnant women, nursing mothers). However, care should also be taken when feeding SWD to dairy cows because, in the present study, milk I concentrations were particularly high and could result in I intakes that pose a health risk for children consuming milk.

Dairy food consumption is beneficially linked with iodine status in US children and adults: National Health and Nutrition Examination Surveys 2001-2018

OBJECTIVES

The objective of this study was to determine the association between the consumption of dairy foods with urinary iodine concentration (UIC) and iodine deficiency risk in a nationally representative sample of the US population.

DESIGN, SETTING AND PARTICIPANTS

24-hour dietary recall data and laboratory data for UIC (μg/l) from subjects 2+ years old US population participating in National Health and Nutrition Examination Surveys 2001-2018 were used (n 26 838) for analyses after adjusting for demographic covariates. Significant associations were assessed at P < 0·05.

RESULTS

Mean intakes of total dairy were 2·21, 2·17 and 1·70 cup equivalents (cup eq) among those 2-8, 9-18 and 19+ years, respectively. Of the dairy components, intake of milk was highest followed by cheese and yogurt for all age groups. Total dairy intakes were positively associated with UIC among those 2-8 years (β = 29·9 ± 9·9 μg/l urine/cup eq dairy) and 9-18 years (β = 26·0 ± 4·8 μg/l urine/cup eq dairy) but not associated among those 19+ years. Total dairy intakes were associated with lowered risks (30 %, 21 % and 20 % for among 2-8, 9-18 and 19+ years, respectively) of being classified as iodine insufficient (UIC < 100 μg/l) or lowered risk (47 %, 30 % and 26 % among 2-8, 9-18 and 19+ years, respectively) of being classified as iodine severely deficient (UIC < 20 μg/l).

CONCLUSIONS

The results indicate that dairy foods are beneficially associated with UIC and lowered iodine deficiency risk.

Plant-Based Dairy Alternatives Contribute to a Healthy and Sustainable Diet

Plant-based foods are increasing in popularity as more and more people are concerned about personal and planetary health. The consumption of plant-based dairy alternatives (PBDAs) has assumed a more significant dietary role in populations shifting to more sustainable eating habits. Plant-based drinks (PBDs) made from soya and other legumes have ample protein levels. PBDs that are appropriately fortified have adequate levels of important vitamins and minerals comparable to dairy milk. For the PBDs examined, the greenhouse gas emissions were diminished by 59-71% per 250 mL, and the land use and eutrophication impact was markedly less than the levels displayed by dairy milk. The water usage for the oat and soya drinks, but not rice drinks, was substantially lower compared to dairy milk. When one substitutes the 250 mL serving of dairy milk allowed within the EAT Lancet Planetary Health Diet for a fortified plant-based drink, we found that the nutritional status is not compromised but the environmental footprint is reduced. Combining a nutrient density score with an environmental index can easily lead to a misclassification of food when the full nutrition profile is not utilized or only a selection of environmental factors is used. Many PBDAs have been categorized as ultra-processed foods (UPFs). Such a classification, with the implied adverse nutritional and health associations, is inconsistent with current findings regarding the nutritional quality of such products and may discourage people from transitioning to a plant-based diet with its health and environmental advantages.

Large Iodine Variability in Retail Cows' Milk in the U.S.: A Follow-Up Study among Different Retail Outlets

In a previous study, large variability in iodine content was found among samples of store brand retail milk at a single time point in a sampling taken from 24 nationwide U.S. locations for the USDA FoodData Central database, but the sampling plan was not designed to detect differences among locations. This follow-up study was carried out to evaluate iodine levels in retail milk across the U.S. over time. Milk samples (2% fat) were collected bimonthly in fourteen locations for one year and analyzed in duplicate. Control materials were used to support accuracy of results and ensure precision across analytical batches. The overall mean and standard error (SE) for iodine concentration were 82.5 (7.0) µg/240 mL serving, which was comparable to the previous national mean [85.0 (5.5) µg/240 mL]. A similar wide range among individual samples was detected (27.9-282 µg/240 mL). For some locations, the mean iodine concentration differed significantly from others, and differed from the national average by amounts ranging from -47 µg to +37 µg per serving. The between-sample range within location was large for some (up to 229 µg/serving) and minimal for others (as little as 13.2 µg/serving). These findings suggest iodine intake from some retail milk supplies could be over- or underestimated relative to the national average, even if the national average is suitable for population-wide intake estimates.

Invited review: Iodine level in dairy products-A feed-to-fork overview

The theme of iodine in the dairy sector is of particular interest due to the involvement and the interconnection of several stakeholders along the dairy food chain. Iodine plays a fundamental role in animal nutrition and physiology, and in cattle it is an essential micronutrient during lactation and for fetal development and the calf's growth. Its correct use in food supplementation is crucial to guarantee the animal's recommended daily requirement to avoid excess intake and long-term toxicity. Milk iodine is fundamental for public health, being one of the major sources of iodine in Mediterranean and Western diets. Public authorities and the scientific community have made great efforts to address how and to what extent different drivers may affect milk iodine concentration. The scientific literature concurs that the amount of iodine administered through animal feed and mineral supplements is the most important factor affecting its concentration in milk of most common dairy species. Additionally, farming practices related to milking (e.g., use of iodized teat sanitizers), herd management (e.g., pasture vs. confinement), and other environmental factors (e.g., seasonality) have been identified as sources of variation of milk iodine concentration. Overall, the aim of this review is to provide a multilevel overview on the mechanisms that contribute to the iodine concentration of milk and dairy products.

Adequacy of total usual micronutrient intakes among pregnant women in the United States by level of dairy consumption, NHANES 2003-2016

Background: Dairy products are a rich source of nutrients of public health concern, though most women do not meet the recommended intake of 3 cup-eq/day. Aim: The objective of this analysis was to examine micronutrient adequacy among pregnant women in the US by level of dairy consumption. Methods: Pregnant women (n  =  791) ages 20-44 years in NHANES 2003-2016 were categorized by level of dairy consumption (<1, 1 to <2, 2 to <3, and ≥3 cup-eq/day). Usual micronutrient intakes and prevalence of intakes below the Estimated Average Requirement (EAR) or above the Adequate Intake level (AI) were calculated from food alone and food plus dietary supplements using the National Cancer Institute method. Diet quality was assessed with the Healthy Eating Index 2015 (HEI-2015). Results: Pregnant women consuming ≥3 cup-eq/day of dairy were more likely to meet the potassium AI than women consuming lower levels. Compared to women consuming ≥3 cup-eq/day of dairy, women consuming <1 or 1 to <2 cup-eq/day were more likely to have inadequate intake of vitamin D, magnesium, zinc, and vitamin A from foods plus supplements. Compared to women consuming ≥3 cup-eq/day of dairy, women consuming <1 cup-eq/day were more likely to have inadequate intake of calcium and riboflavin. The median urinary iodine concentration (UIC) among pregnant women consuming ≥3 cup-eq/day of dairy was 220 ng/mL compared with median UICs of 98-135 mg/mL among women consuming the lowest levels. Pregnant women consuming ≥3 cup-eq/day of dairy had the highest intake of sodium (mg/day) and saturated fat intake evaluated as a HEI-2015 component. Conclusions: Consumption of recommended levels of dairy products may help pregnant women achieve adequate intakes of select micronutrients.

Trends in Iodine Status Among U.S. Children and Adults: A Cross-Sectional Analysis of National Health and Nutrition Examination Survey Data from 2001-2004 to 2017-2020

Background: Iodine nutrition is an important public health issue. Trends in iodine status over time among U.S. schoolchildren and adults and factors mediating changes of iodine status were examined. Methods: In this cross-sectional study of National Health and Nutrition Examination Survey (NHANES) data, we estimated trends in the U.S. population using linear regression analyses. Representative samples of U.S. children and adults were enrolled in NHANES 2001-2020. The NHANES cycles were categorized into 5 four-year periods: 2001-2004, 2005-2008, 2009-2012, 2013-2016, and 2017-2020. The final sample sizes of children and adults for analysis were 4288 and 19,661, respectively. The estimated average requirement (EAR) (based on guidelines from the Institute of Medicine), was used to estimate the prevalence rate of inadequate iodine intake. Binary logistic regression analyses were used to investigate the association between iodine status and contributing factors. Results: From 2001-2004 to 2017-2020, among children, urinary iodine concentration (UIC) decreased from 243 to 166 μg/L (p_trend = 0.0057) and prevalence of iodine intake below the EAR rose from 15.4% to 27.6%. In adults, the UIC decreased from 153 to 116 μg/L (p_trend < 0.001) and prevalence of iodine intake below the EAR rose from 15.0% to 17.9%. A higher prevalence rate of iodine intake below the EAR was observed in females compared with males (children, 24.0% vs. 16.5%, p < 0.001; adults, 20.0% vs. 11.1%, p < 0.001). Inadequate iodine intake was less frequent among non-Hispanic White and Hispanic compared with non-Hispanic Black in children and adults. Adults without thyroid problems had a higher prevalence of inadequate iodine intake than those with thyroid problems (16.0% vs. 13.0%, p = 0.001). Inadequate iodine intake was less likely in the children who "sometimes" and "often" consumed milk products compared with children who "never or rarely" consumed milk products (OR = 0.60 [CI 0.30-1.21] and OR = 0.24 [CI 0.13-0.43], respectively). The prevalence of inadequate iodine intake among adults reporting "sometimes" (OR = 0.70 [CI 0.58-0.83]) and "often" consuming milk products was lower than those who "never or rarely" consumed them (OR = 0.36 [CI 0.30-0.44]). Conclusions: In this weighted survey, the prevalence of inadequate iodine intake increased from 2001-2004 to 2017-2020 among U.S. school-age children and adults. Sex, race, thyroid problems, and a decreased intake of milk products were significantly associated with iodine intake below the EAR.

The Prevalence and Risk Factors Associated with Iodine Deficiency in Canadian Adults

Iodine is a trace micronutrient that is critical for normal thyroid function and human health. Inadequate dietary intake is associated with cognitive impairment, infertility, growth retardation and iodine deficiency disorders in affected populations. Herein, we examined the prevalence of iodine deficiency in adults (median age of 61 years) based on the analysis of 24 h urine samples collected from 800 participants in four clinical sites across Canada in the Prospective Urban and Rural Epidemiological (PURE) study. Urinary iodide together with thiocyanate and nitrate were measured using a validated capillary electrophoresis assay. Protective/risk factors associated with iodine deficiency were identified using a binary logistic regression model, whereas daily urinary iodine concentration (24 h UIC, μg/L) and urinary iodine excretion (24 h UIE, μg/day) were compared using complementary statistical methods with covariate adjustments. Overall, our Canadian adult cohort had adequate iodine status as reflected by a median UIC of 111 μg/L with 11.9% of the population <50 μg/L categorized as having moderate to severe iodine deficiency. Iodine adequacy was also evident with a median 24 h UIE of 226 μg/day as a more robust metric of iodine status with an estimated average requirement (EAR) of 7.1% (< 95 μg/day) and a tolerable upper level (UL) of 1.8% (≥1100 μg/day) based on Canadian dietary reference intake values. Participants taking iodine supplements (OR = 0.18; p = 6.35 × 10−5), had greater 24 h urine volume (OR = 0.69; p = 4.07 × 10−4), excreted higher daily urinary sodium (OR = 0.71; p = 3.03 × 10−5), and/or were prescribed thyroxine (OR = 0.33; p = 1.20 × 10−2) had lower risk for iodine deficiency. Self-reported intake of dairy products was most strongly associated with iodine status (r = 0.24; p = 2.38 × 10−9) after excluding for iodine supplementation and T4 use. Participants residing in Quebec City (OR = 2.58; p = 1.74 × 10−4) and Vancouver (OR = 2.54; p = 3.57 × 10−4) were more susceptible to iodine deficiency than Hamilton or Ottawa. Also, greater exposure to abundant iodine uptake inhibitors from tobacco smoking and intake of specific goitrogenic foods corresponded to elevated urinary thiocyanate and nitrate, which were found for residents from Quebec City as compared to other clinical sites. Recent public health policies that advocate for salt restriction and lower dairy intake may inadvertently reduce iodine nutrition of Canadians, and further exacerbate regional variations in iodine deficiency risk.

Development of Food Pattern Recommendations for Infants and Toddlers 6-24 Months of Age to Support the Dietary Guidelines for Americans, 2020-2025

BACKGROUND

Developing food-based dietary guidelines (FBDGs) for infants and toddlers is a complex task that few countries have attempted.

OBJECTIVES

Our objectives are to describe the process of food pattern modeling (FPM) conducted to develop FBDGs for the Dietary Guidelines for Americans, 2020-2025 for infants 6 to <12 mo and toddlers 12 to <24 mo of age, as well as the implications of the results and areas needing further work.

METHODS

The US 2020 Dietary Guidelines Advisory Committee, with the support of federal staff, conducted FPM analyses using 5 steps: 1) identified energy intake targets; 2) established nutritional goals; 3) identified food groupings and expected amounts, using 3 options for the amount of energy from human milk in each age interval; 4) estimated expected nutrient intakes for each scenario, based on nutrient-dense representative foods; and 5) evaluated expected nutrient intakes against nutritional goals.

RESULTS

For human milk-fed infants (and toddlers), example combinations of complementary foods and beverages were developed that come close to meeting almost all nutrient recommendations if iron-fortified infant cereals are included at 6 to <12 mo of age. These combinations would also be suitable for formula-fed infants. For toddlers not fed human milk, 2 patterns were developed: the Healthy US-Style Pattern and the Healthy Vegetarian Pattern (a lacto-ovo vegetarian pattern). Achieving nutrient recommendations left virtually no remaining energy for added sugars.

CONCLUSIONS

It is challenging to meet all nutrient needs during these age intervals. Added sugars should be avoided for infants and toddlers <2 y of age. Further work is needed to 1) establish a reference human milk composition profile, 2) update and strengthen the DRI values for these age groups, and 3) use optimization modeling, in combination with FPM, to identify combinations of foods that meet all nutritional goals.

Iodine Content in Meal Replacements in the United States

OBJECTIVE

Iodine is essential for thyroid hormone production. The recommended dietary allowance for iodine in nonpregnant adults is 150 μg/d. However, most product labels do not list the iodine content. Meal replacements are not required to contain specific vitamins and minerals. Nevertheless, they are often marketed as good and convenient sources of a balanced nutrition. In this study, we aimed to assess the iodine content in meal replacements to determine how they may contribute to iodine deficiency or excess.

METHODS

Twenty seven meal replacements from supermarkets in the Boston area were collected. The iodine concentration of each meal replacement was measured spectrophotometrically. Iodine content in meal replacements were compared according to form (liquid, bar, and powder) and type (vegan and nonvegan).

RESULTS

The overall mean ± SD iodine content was 49.7 ± 125.4 μg/serving. However, 1 meal replacement was an outlier and had 671.9 μg iodine per serving. Mean iodine content differed between forms and was highest for liquids (mean ± SD: 37.4 ± 6.5 μg/serving). Nonvegan meal replacements had a higher mean iodine content than vegan meal replacements (mean ± SD: 31.6 ± 15.78 μg/serving).

CONCLUSION

All of the meal replacements contained detectible amounts of iodine regardless of whether it was listed on their labels (41% did not list iodine). Overall, the meal replacements in this study were found to be good sources of iodine. However, consumers should be aware that packaging labels may not accurately reflect the amount of iodine present.

Nutritional Quality of Plant-Based Drinks Sold in Italy: The Food Labelling of Italian Products (FLIP) Study

Plant-based drinks represent a heterogeneous class of beverages, made from several vegetal sources, with a market rapidly expanding around the world. These beverages are mainly drunk in the replacement of milk. Thus, aims of the present study were to: (i) evaluate the nutritional declaration of 330 plant-based drinks currently available on the Italian market; (ii) compare their nutrition facts based on type, presence or not of organic certification and nutrition (NC) or health claims (HC), and of specific claims ("no added sugars" and "source of calcium"); (iii) compare their nutrition composition with cow's milk. A high variability in terms of nutrient profile among products was observed. Limited difference was found between products belonging to both organic and NC categories, while products carrying HC showed lower energy, carbohydrates, sugar, and higher protein contents than the related counterparts. Compared to cow's milk, plant-based drinks showed differences in terms of nutrient profile, mostly regarding the lower protein content (except for soy drinks). Overall, due to the variability, findings from the present survey show that plant-based drinks sold in Italy cannot be considered tout court as milk substitutes and support the importance of improving knowledge towards food labeling to make conscious food choices.