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VITAMIN D INSUFFICIENCY AND FACTORS ASSOCIATED: A STUDY WITH OLDER ADULTS PEOPLE FROM PRIMARY HEALTH CARE NETWORK

Patricia Moreira Donato Rolizola
Faculdade de Ciências Aplicadas - FCA/UNICAMP-SP
pmdonator@gmail.com
ORCID: https://orcid.org/0000-0001-9463-8686

Carolina Neves Freiria
Faculdade de Ciências Médicas - FCM/UNICAMP-SP
carol_freiria@hotmail.com
ORCID: https://orcid.org/0000-0002-1493-3202

Graziele Maria da Silva
Faculdade de Ciências Aplicadas - FCA/UNICAMP-SP
gra_sml@hotmail.com
ORCID: https://orcid.org/0000-0003-0634-275X
Tabatta Renata Pereira de Brito
Faculdade de Nutrição da Universidade Federal de Alfenas/UNIFAL-MG
tabatta_renata@hotmail.com
ORCID: https://orcid.org/0000-0001-9466-2993

Flávia Silva Arbex Borim
Departamento de Saúde Coletiva da Faculdade de Ciências da Saúde/UNB
flarbex@hotmail.com
ORCID: https://orcid.org/0000-0001-7316-1145

Ligiana Pires Corona
Faculdade de Ciências Aplicadas - FCA/UNICAMP-SP
ligiana.corona@fca.unicamp.br
ORCID: https://orcid.org/0000-0001-5298-7714

ABSTRACT
Objectives: Analyze vitamin D insufficiency and factors associated among older adults using primary health care services. Methods: This is a cross-sectional study that evaluated 533 older adults individuals (≥60 years old) in three cities in the state of São Paulo, Brazil. Serum level of 25-hydroxyvitamin D (25-OHD) was evaluated by chemiluminescence (values <30ng/mL were considered insufficiency). The factors evaluated were sociodemographic information (sex, age group, ethnicity, education, income, marital status), health conditions (reported diseases), body composition (BMI, waist circumference), lifestyle (physical activity and smoking), and sun exposure (purpose, duration, frequency, time of exposure, exposed body parts, use of sunscreen, skin type). Results: The prevalence of vitamin D insufficiency was 64.5%, presenting association with female participants, non-white/unreported ethnicity, low weight, high waist circumference (risk for CVD – cardiovascular disease), and physical inactivity. Negative association was observed with habitual sun exposure of hands, arms and legs, during leisure activities, daily commuting and physical activity, and between 9 am and 3 pm. Conclusion: The findings show the relevance of factors such as sex, ethnicity, body composition, physical activity, and sun exposure habits in the high prevalence of inadequate levels of vitamin D among older adults.
Keywords: Older adults; Vitamin D; Sun exposure; Public health.

INTRODUCTION
Vitamin D has a very clear role in bone mineralization; it has been highlighted for its complex activity in the body, including control of metabolic processes. Proper levels of vitamin D are suggested to help protect the body against musculoskeletal disorders, infectious diseases, cancers, autoimmune and cardiovascular diseases, diabetes mellitus, and neurocognitive dysfunctions, with low serum concentrations of vitamin D related to increased risk for development and progression of these diseases1.
Cutaneous synthesis regulated by sunlight is the main source of vitamin D in humans, so there is a false impression that vitamin D deficiency is not a problem in sunny countries, and for this reason, serum concentrations of vitamin D in the population are not often measured. However, according to studies conducted in Brazil and other countries, hypovitaminosis D is highly prevalent, regardless of the region evaluated, with Brazilian studies showing prevalence ranging from 28.5% according to a study conducted with hypertensive older adults in João Pessoa, Paraíba, in spring and summer, to almost 96%, as reported in another study that evaluated older adults in São Paulo, SP, in winter2.
A study by Cabral et al.3, which evaluated 234 older adults male individuals in Recife, Pernambuco, in summer, found 66.7% prevalence of vitamin D insufficiency, with mean serum concentrations of 25-hydroxyvitamin D below the recommended level (27.86±13.52ng/mL). These mean values are similar to those found in another recent study4 conducted with 287 older adults from a community in Palhoça, Santa Catarina (26.09±9.20ng/mL).
In addition to sun exposure, many other factors may be involved in vitamin D deficiency, such as age, skin pigmentation, obesity, multimorbidity, and use of certain medications like antihypertensive, anticonvulsant, anti-inflammatory, and sedative medications. Due to lifestyle habits, polypharmacy, multimorbidity, and reduced effectiveness of vitamin D production in the skin, the older adults are one of the most important groups at risk for vitamin D deficiency5.
In this context, considering that few studies have assessed representative samples of older adults in primary health care in Brazil6,7, and knowing that serum vitamin D is not widely tested in the older adults population using primary health care services, factors must be identified for an early identification of vitamin D insufficiency, enabling actions and strategies to prevent and control this condition, which has become more prevalent in Brazil and worldwide. This study aims to analyze the prevalence of vitamin D insufficiency and its association with sociodemographic variables, sun exposure habits, physical and health conditions in older adults using primary health care services.
METHODS
Participants
This is a cross-sectional study, which is part of a larger study titled “Evaluation on the prevalence of micronutrient deficiency in older adults living in cities in the region of Campinas - SP,” conducted in the municipalities of Limeira, Piracicaba, and Campinas, in the state of São Paulo, Brazil.
The inclusion criteria for study participation were: aged 60 years and older, living in one of the study municipalities, and presenting proper neurological and cognitive conditions to answer the questionnaires (as assessed by the interviewer during the study presentation and invitation to participate). Exclusion criteria were: use of food supplements based on vitamins and/or minerals, participation in a home care program, and receiving chemotherapy treatment.
The study sample was estimated considering the total number of inhabitants aged 60 years and older in the municipalities of Campinas, Limeira, and Piracicaba using official data of population estimates for 2018 and considering a prevalence of 60% of older adults with deficiency of at least one of the evaluated nutrients, considering a sampling error of 10% and 95% confidence level. Then, the total sample was 600 older adults, with 250 participants from the city of Campinas, 170 from Limeira, and 180 from Piracicaba.
Data were collected from 612 participants from October 2018 to December 2019 (no data collection was performed during the winter); 17 individuals had incomplete data and 62 who reported using supplements containing vitamin D were excluded, so the final sample had 533 individuals.
The older adults volunteers were recruited through an invitation made at the basic health units (UBS) recommended by the respective Health Departments of each municipality.
This study was approved by the Ethics Committee for Research with Human Beings from Universidade Estadual de Campinas, study approval nº 2.878.652 and CAAE 95607018.8.0000.5404. All participants signed an informed consent form.
Data collection
In each selected health unit, the older adults patients were invited by the research team to participate in the study and instructed to come back on the scheduled date with at least 8-hour fasting. On the scheduled day, a blood sample was collected, anthropometric data were measured, and then an interview was conducted to answer the questionnaire. These procedures were performed by a team of undergraduate and graduate health students, previously trained by the research coordinators.
Study variables
The dependent variable of the study was vitamin D insufficiency. Serum vitamin D levels were analyzed by measuring 25-hydroxyvitamin D (25-OHD) using the chemiluminescence immunoassay technique, with the Alinity 25-OH Vitamin D reagent kit (Abbott®). The tubes containing collected blood were stored in a cooler with ice, and immediately at the end of collection, they were sent to the same private laboratory hired for this study (Pasteur®), where the samples were processed and then analyzed (no freezing). For serum 25-hydroxyvitamin D levels, the reference values recommended by Brazilian Society of Endocrinoloy and Metabology (SBEM) and Brazilian Society of Clinical Pathology/Laboratory Medicine (SBPC)8 were used, so values below 30 ng/ml were considered vitamin D insufficiency.
The study covariates were: sex, age group, ethnicity, monthly income, physical activity, smoking, self-reported diseases, body mass index (BMI), waist circumference, sun exposure, use of sunscreen, sun exposure time, part of the body exposed to the sun, duration of sun exposure, frequency of sun exposure, and skin types.
BMI is a person’s body weight (in kilograms) divided by the square of height (in meters). Weight was measured with the individual standing on an electronic weighing scale (150 kg capacity, 50 gram accuracy). Height was measured using a professional portable stadiometer, 0.1 cm accuracy, where the individual was standing straight with heels together on the base. BMI of the participants was classified according to the cutoff points for the older adults, as recommended by the Ministry of Health9, that is, up to 22 kg/m2: low weight, between 22 and 26.99 kg/m2: eutrophic, 27 kg/m2 or more: overweight.
Waist circumference was measured with a non-extendable measuring tape located at the midpoint between the iliac crest and the last rib. Risk for cardiovascular disease (CVD) was considered when the male participants presented 102 centimeters or more and 88 centimeters or more for female participants10.
Regarding physical activity, individuals were considered active when they reported at least 150 minutes of moderate intensity aerobic physical activity or 75 minutes of vigorous intensity aerobic physical throughout the week11.
For the assessment of smoking, individuals answered “yes” if they were currently smokers, “no” if they had never smoked, or if they were former smokers.
Skin type was assessed using the Fitzpatrick scale12, which defines scores to skin phototypes: from 1 to 6, where type 1 is the palest skin which always burns and never tans, and type 6 is the darkest skin which never burns and always tans when exposed to the sun (the participant pointed to a printed picture matching the color of his/her skin).
Statistical analysis
For the statistical analysis of the study variables, distributions of relative frequencies, mean values and standard deviation were estimated for continuous variables, and proportions were estimated for categorical variables. Differences between groups were estimated using the Mann-Whitney test after analyzing the normality of distributions, and x2 test was used to analyze differences between categorical variables. Variables with p value <0.20 in simple association were selected to calculate crude and age-adjusted odds ratios, with different models for general, physical and health characteristics and sun exposure habits, but the variables with p value <0.05 remained in the tables. The critical level was p <0.05. The analyses were performed in Stata® version 14.
RESULTS
All 533 participants included in the study had a mean age of 69.6±6.7 years, with predominance of female participants. Most participants were married (60.4%), white (54.4%), had less than 8 years of education (71.8%) and income of two or more minimum wages (70.5%). When analyzing the nutritional status indicators, we found mean BMI of 28.9±5.4 kg/m2, with most participants classified as overweight (60.4%) and at risk for CVD according to the waist circumference assessment (58.7%). Regarding health-related behaviors, 58.7% had never smoked and 64.4% were inactive smokers (Table 1).
The mean serum concentration of 25-OHD was 28.3±9.2 ng/mL, and the prevalence of insufficiency was 64.5%, higher among female participants and those who self-reported as black/brown/indigenous/yellow/unreported, categorized as “other” ethnicity (Table 1). No difference was observed in age group, marital status, income, education, those with paid work, and head of household. Table 1 shows higher prevalence of vitamin D insufficiency among individuals classified as underweight and those with a waist circumference measurement above the limits of risk for developing CVD.
Regarding health data of participants, most of them reported medical diagnosis of 3 or more diseases – the most prevalent disorders were: hypertension (61.9%), spine issues (50.5%), rheumatism (43.1%), diabetes (27.6%), depression (27.6%), and CVD (23.6%). No significant difference was found when associating these diseases and vitamin D insufficiency or grouping individuals by the number of pre-existing diseases.
In the evaluation of sex- and age-adjusted logistic regression of general, physical and health characteristics of participants, those of “other” ethnicity, low weight and high waist circumference were more likely to have vitamin D insufficiency (Table 2).
Table 3 shows that most participants self-reported daily sun exposure while commuting (e.g., going to the market, drugstore, etc.) without sunscreen. They also reported exposure of less than 3 times during the week, for less than 15 minutes on average, between 9 am and 3 pm, with hands, arms and face as their more frequently exposed body parts. Every participant could report more than one exposure habit, time and exposed body parts. According to the Fitzpatrick scale, the predominant skin phototype was type 4, followed by types 2 and 3.
The proportion of vitamin D sufficiency was higher among participants reporting sun exposure during leisure and physical activities (p=0.018 and p=0.010, respectively). A difference was also observed between participants who reported exposure between 9 am and 3 pm (p=0.032) and exposure of hands and arms (p=0.046) (Table 3).
In the evaluation of sex- and age-adjusted logistic regression of sun exposure habits of participants, a negative association was observed between vitamin D insufficiency and individuals reporting exposure habits during leisure activities, daily commuting, practice of physical activities, exposure between 9 am and 3 pm, and hands, arms and as their more frequently exposed body parts (Table 4).
DISCUSSION
A high prevalence of vitamin D insufficiency was reported among the older adults participants evaluated (64.5%), with sex, ethnicity, body composition and some habits of sun exposure associated with vitamin D insufficiency.
Regarding the high prevalence of vitamin D insufficiency, similar indices were found in another study conducted with the same population profile in the country4,13,14, while a study performed with 81 older adults in Ribeirão Preto, São Paulo15, found a higher prevalence (76.5%) of vitamin D insufficiency, with serum 25-OHD levels of 24.63±7.89 ng/mL.
Brazil has a geographic location that provides good availability of ultraviolet rays (UVB) throughout the year, which allows exposure to sunlight and cutaneous synthesis of vitamin D at proper concentrations in most seasons of the year. However, studies have reported high prevalence of vitamin D insufficiency and deficiency. This paradox can be partly explained by the concern about preventing high levels of sun exposure, regardless of the concentration of solar radiation, a precaution that leads the population to be less exposed to the sun or use physical/chemical barriers (clothes, hats, sunscreen), thus increasing the prevalence of inadequate levels of vitamin D16.
Specifically in relation to sex, the female participants had lower mean values and higher prevalence of insufficiency (adjusted OR 2.54; p<0.001). A study that evaluated 359 older adults in Teresina, Piauí,7 found even lower mean values when analyzing serum levels (22.51±8.03 ng/mL), which were also lower among female participants. Several studies17–19 show that women are more likely to have lower levels of 25-OHD than men, particularly due to the type of clothes and sun protection behavior of women, which makes cutaneous synthesis of vitamin D less efficient20.
Regarding skin color, reduced efficiency of vitamin D synthesis in people with dark skin is well described in the literature, to the greater amount of melanin, which acts as a natural sunscreen5. It explains the higher prevalence of vitamin D insufficiency found among individuals reporting more pigmented skin color ethnicities.
The association between overweight and vitamin D insufficiency is also well described in the literature21–27. It can be explained by biological factors, since obesity decreases the bioavailability of vitamin D obtained by cutaneous synthesis, as vitamin D tends to be deposited on adipose tissue, changes the regulation of PTH and hepatic synthesis of 25-OHD, and involves lifestyle factors, such as lower intake of vitamin D in the diet of obese people28. Although this study did not find an association with overweight according to the BMI classification, after an adjusted regression analysis, this association was observed with increased waist circumference (adjusted OR 1.57; p=0.018). A study conducted by Snijder et al.21 in Amsterdam with 453 older adults found an association between low levels of 25-OHD and high waist circumference. This characteristic is an important factor, as it seems to make an individual more susceptible to lower levels of 25-OHD29,30.
On the other hand, we found a strong association between vitamin D insufficiency and low weight (adjusted OR 2.56; p=0.023). A study conducted by Cabral31 that assessed older adults in Porto Alegre, Rio Grande do Sul, also found deficient levels of 25-OHD with higher prevalence among thin or malnourished older adults, suggesting vitamin D deficiency is associated with nutritional risk and malnutrition.
Several studies show higher serum levels of 25-OHD among individuals who practice physical activities21,28,32,33. This characteristic is even more accentuated when this practice is performed outdoors19. In this study, we found no significant difference between groups in terms of active individuals. However, individuals reporting sun exposure during physical activity showed a lower prevalence of vitamin D insufficiency.
Among the diseases reported by participants, although the relationship between hypovitaminosis D and various diseases such as diabetes, cardiovascular diseases, hypertension, cancer, osteoporosis, depression, among others34, is well described in the literature, no association was observed between these diseases and vitamin D insufficiency. Also, no significant difference was found regarding the number of diseases reported by participants.
A correctly applied sunscreen with sun protection factor (SPF) 30 is presumed to reduce by 95% to 99% the skin ability to produce vitamin D35. Despite that, we found no significant difference for vitamin D insufficiency between individuals who reported using sunscreen and those who did not have such habit. A similar result was reported by Maeda et al.19 for using sunscreen or not. On the other hand, in a study conducted by Cabral31, sunscreen was significantly associated with proper levels of 25-OHD, a fact that, according to the author, can be explained by a possible application of insufficient or uneven sunscreen.
The efficiency of sun exposure in vitamin D synthesis depends on the use of sunscreen and other factors, such as latitude, season of the year, air pollution, skin pigmentation, and age36. For white adults, it is recommended to expose arms and legs to the sun (which represent 25% of the body surface when wearing shorts and a short-sleeve shirt or blouse) for about 5 to 15 minutes, between 9 am and 3 pm, 3 times a week (depending on the latitude, season of the year, and skin pigmentation), which would be sufficient for the production of vitamin D required. However, among the older adults, cutaneous synthesis is reduced to around 25% of the capacity of a 20-year-old person37.
Despite the reduced capacity of vitamin D photoproduction among older people, Brouwer-Brolsma et al.36 observed significant associations between habitual sun exposure and 25-OHD in this population. Data from a study conducted by Maeda et al.19 suggest the amount of UVB radiation at the latitude of the city of São Paulo, SP, is sufficient for proper production of vitamin D, even for the older population, as long as they have minimal exposure. However, it should be noted that sun exposure is not enough to compensate for vitamin D insufficiency or deficiency 38. Data obtained in this study related to sun exposure agree with literature findings. Lower proportions of vitamin D insufficiency were observed among individuals who reported sun exposure during leisure activities and physical activities (p=0.018 and p=0.010, respectively), and between 9 am and 3 pm, the peak period of solar radiation (p=0.032).
Our study limitation refers to the fact that it used the older adults participants accounts as a parameter to assess habitual sun exposure, and this information can be underestimated or overestimated. Also, data were not analyzed separately by season. However, data collection was not performed during the winter and, considering the incidence of UVB rays are similar during spring, summer and autumn at the latitude in question, we consider these findings to be relevant. Another study limitation is that the individuals were volunteers, and many of them came from health groups from the primary health care system in the municipalities, including outdoor physical activity groups, causing the bias of “healthy participant/volunteer participant,” a fact that may have partially influenced the results. However, this is a common limitation in population studies where participants are invited in out-of-home interviews, as volunteers are usually more interested in health-related issues.
One of the strengths of our study is the assessment of a sample of older population assisted by primary health care services in the cities of Limeira, Piracicaba, and Campinas, and the investigation conducted in the same study of various factors that can be associated with vitamin D insufficiency in this vulnerable age group.
The results obtained show the relevance of the impact of factors like sex, ethnicity, body composition, physical activity, and sun exposure habits on the prevalence of inadequate levels of vitamin D among older adults, and the importance of considering these factors as vitamin D insufficiency predictors in this population, mainly as a primary care tool. The assessment of these factors is a simple, low-cost and non-invasive measure that can contribute to the early identification of vitamin D insufficiency, enabling actions and strategies to prevent and control this condition, which has become increasingly prevalent in Brazil and in the world.
Acknowledgment
The authors thank Espaço da Escrita - Pró-Reitoria de Pesquisa - UNICAMP - for the language services provided.
REFERENCES
1. Wimalawansa SJ. Non-musculoskeletal benefits of vitamin D. J Steroid Biochem Mol Biol. 2018;175:60–81.
2. Mendes MM, Hart KH, Botelho PB, Lanham-New SA. Vitamin D status in the tropics: Is sunlight exposure the main determinant? Nutr Bull. 2018;43(4):428–434.
3. Cabral MA, Borges CN, Maia JMC, Aires CAM, Bandeira F. Prevalence of vitamin D deficiency during the summer and its relationship with sun exposure and skin phototype in elderly men living in the tropics. Clin Interv Aging. 2013;8:1347–1351.
4. Santos C de S dos, Bessa TA de, Xavier AJ. Fatores associados à demência em idosos. Cien Saude Colet. 2020;25(2):603–611.
5. Moreira CA, Ferreira CEDS, Madeira M, Silva BCC, Maeda SS, Batista MC, et al. Reference values of 25-hydroxyvitamin D revisited: a position statement from the Brazilian Society of Endocrinology and Metabolism (SBEM) and the Brazilian Society of Clinical Pathology/Laboratory Medicine (SBPC). Arch Endocrinol Metab. 2020;64(4):462–478.
6. Oliveira GBVP de, Nunes IF de OC, Carvalho LR, Figueirêdo RG, Oliveira M da CB, Carvalho CMRG de. Perfil antropométrico e níveis séricos de vitamina D de idosos participantes do programa saúde da família de Teresina. Rev Interd Ciên Saúde. 2014;1(1):48–55.
7. Oliveira GBVP de, Silva Júnior FL e, Oliveira M da CB, Carvalho CMRG de. Relação dos índices antropométricos e vitamina D com o desempenho funcional em idosos TT - Relationship of anthropometric indices and vitamin D with functional performance in elderly. Estud interdiscip Envelhec. 2018;23(1):43–59.
8. Ferreira CES, Maeda SS, Batista MC, Lazaretti-Castro M, Vasconcellos LS, Madeira M, et al. Consensus – reference ranges of vitamin D [25(OH)D] from the Brazilian medical societies. Brazilian Society of Clinical Pathology/Laboratory Medicine (SBPC/ML) and Brazilian Society of Endocrinology and Metabolism (SBEM). J Bras Patol e Med Lab. 2017;56(6):377–81.
9. Brasil. Ministério da Saude. Orientações para a coleta e análise de dados antropométricos em serviços de saúde : Norma Técnica do Sistema de Vigilância Alimentar e Nutricional - SISVAN. Secr Atenção à Saúde Dep atenção Básica. 2011;
10. Who WHO. WHO 1995 PHYSICAL STATUS. USE AND ANTHROPOMETRY. World Health Organization technical report series. 1995.
11. Who WHO. Global recommendations on physical activity for health. Geneva World Heal Organ. 2010;
12. Fitzpatrick TB. The Validity and Practicality of Sun-Reactive Skin Types I Through VI. Arch Dermatol. 1988;124(6):869–71.
13. Saraiva GL, Cendoroglo MS, Ramos LR, Araújo LMQ, Vieira JGH, Kunii I, et al. Influence of ultraviolet radiation on the production of 25 hydroxyvitamin D in the elderly population in the city of São Paulo (23° 34’S), Brazil. Osteoporos Int. 2005;16(12):1649–54.
14. Saraiva GL, Cendoroglo MS, Ramos LR, Araújo LMQ, Vieira JGH, Maeda SS, et al. Prevalência da deficiência, insuficiência de vitamina D e hiperparatiroidismo secundário em idosos institucionalizados e moradores na comunidade da cidade de São Paulo, Brasil. Arq Bras Endocrinol Metabol. 2007;51(3):437–42.
15. Cicilini AL, Singling MV, da Silva KA, Ramos APP. Níveis séricos de 25-hidroxivitamina D em idosos com Diabetes mellitus tipo 2 atendidos em um Hospital Universitário de Ribeirão Preto (SP). Rev Ciências da Saúde da Amaz. 2019;1:3–24.
16. Pereira-Santos M, Santos JYG dos, Carvalho GQ, Santos DB dos, Oliveira AM. Epidemiology of vitamin D insufficiency and deficiency in a population in a sunny country: Geospatial meta-analysis in Brazil. Crit Rev Food Sci Nutr. 2019;59:2102–2109.
17. Dawson-Hughes B, Harris SS, Dallal GE. Plasma calcidiol, season, and serum parathyroid hormone concentrations in healthy elderly men and women. Am J Clin Nutr. 1997;65(1):67–71.
18. Carnevale V, Modoni S, Pileri M, Di Giorgio A, Chiodini I, Minisola S, et al. Longitudinal evaluation of vitamin D status in healthy subjects from southern Italy: Seasonal and gender differences. Osteoporos Int. 2001;12(12):1026–30.
19. Maeda SS, Kunii IS, Hayashi LF, Lazaretti-Castro M. Increases in summer serum 25-hydroxyvitamin D (25OHD) concentrations in elderly subjects in São Paulo, Brazil vary with age, gender and ethnicity. BMC Endocr Disord. 2010;10.
20. Nimitphong H, Holick MF. Vitamin D status and sun exposure in Southeast Asia. Dermatoendocrinol. 2013;5(1):34–7.
21. Snijder MB, Van Dam RM, Visser M, Deeg DJH, Dekker JM, Bouter LM, et al. Adiposity in relation to vitamin D status and parathyroid hormone levels: A population-based study in older men and women. J Clin Endocrinol Metab. 2005;90(7):4119–23.
22. Scragg R, Camargo CA. Frequency of leisure-time physical activity and serum 25-hydroxyvitamin D levels in the US population: Results from the third national health and nutrition examination survey. Am J Epidemiol. 2008;168(6):577–86.
23. Lagunova Z, Porojnicu LC, Lindberg F, Hexeberg S, Moan J. The dependency of vitamin D status on body mass index, gender, age and season. In: Anticancer Research. 2009. p. 3713–20.
24. Jorde R, Sneve M, Emaus N, Figenschau Y, Grimnes G. Cross-sectional and longitudinal relation between serum 25-hydroxyvitamin D and body mass index: The Tromsø study. Eur J Nutr. 2010;49(7):401–7.
25. Yoshimura N, Muraki S, Oka H, Morita M, Yamada H, Tanaka S, et al. Profiles of vitamin D insufficiency and deficiency in Japanese men and women: Association with biological, environmental, and nutritional factors and coexisting disorders: The ROAD study. Osteoporos Int. 2013;24(11):2775–87.
26. Nakamura K, Kitamura K, Takachi R, Saito T, Kobayashi R, Oshiki R, et al. Impact of demographic, environmental, and lifestyle factors on vitamin D sufficiency in 9084 Japanese adults. Bone. 2015;74:10–7.
27. Mansouri M, Abasi R, Nasiri M, Sharifi F, Vesaly S, Sadeghi O, et al. Association of vitamin D status with metabolic syndrome and its components: A cross-sectional study in a population of high educated Iranian adults. Diabetes Metab Syndr Clin Res Rev. 2018;12(3):393–8.
28. Jääskeläinen T, Knekt P, Marniemi J, Sares-Jäske L, Männistö S, Heliövaara M, et al. Vitamin D status is associated with sociodemographic factors, lifestyle and metabolic health. Eur J Nutr. 2013;52(2):513–25.
29. Gheno FP, Cabral MMS, Schirmer CL, Dallepiane LB, Bos AJG. Diet Quality and Nutritional Status in Southern Brazilian Oldest Old. Nutr Food Toxicol. 2017;1(2).
30. Matchar DB, Chei CL, Yin ZX, Koh V, Chakraborty B, Shi XM, et al. Vitamin D Levels and the Risk of Cognitive Decline in Chinese Elderly People: The Chinese Longitudinal Healthy Longevity Survey. Journals Gerontol - Ser A Biol Sci Med Sci. 2016;71(10):1363–8.
31. Cabral MMS. VITAMINA D EM LONGEVOS, QUAL O FATOR MAIS IMPORTANTE: INGESTA ALIMENTAR OU EXPOSIÇÃO SOLAR? [Internet]. Pontifícia Universidade Católica do Rio Grande do Sul; 2017. Available at: http://tede2.pucrs.br/tede2/bitstream/tede/8825/2/CABRAL_MARIA_MARINA_SERRAO_TES.pdf
32. Looker AC. Do Body Fat and Exercise Modulate Vitamin D Status? Nutr Rev. 2007;65(SUPPL.2).
33. Hintzpeter B, Mensink GBM, Thierfelder W, Müller MJ, Scheidt-Nave C. Vitamin D status and health correlates among German adults. Eur J Clin Nutr. 2008;62(9):1079–89.
34. Caristia S, Filigheddu N, Barone-Adesi F, Sarro A, Testa T, Magnani C, et al. Vitamin D as a biomarker of ill health among the over-50s: A systematic review of cohort studies. Nutrients. 2019;11.
35. Hossein-Nezhad A, Holick MF. Vitamin D for health: A global perspective. In: Mayo Clinic Proceedings. 2013. p. 720–55.
36. Brouwer-Brolsma EM, Vaes AMM, van der Zwaluw NL, van Wijngaarden JP, Swart KMA, Ham AC, et al. Relative importance of summer sun exposure, vitamin D intake, and genes to vitamin D status in Dutch older adults: The B-PROOF study. J Steroid Biochem Mol Biol. 2016;164:168–176.
37. Holick MF. Vitamin D: A D-lightful solution for health. In: Journal of Investigative Medicine. 2011. p. 872–80.
38. Lee YM, Kim SA, Lee DH. Can current recommendations on sun exposure sufficiently increase serum vitamin D level?: One-month randomized clinical trial. J Korean Med Sci. 2020;35(8).