Research shows that 25(OH)D deficiency is a widespread problem across the world, with many people in Ecuador being affected. A meta-analysis of 165 studies from 65 countries found that 76.6% of participants had a serum 25(OH)D level of below 30 ng/mL, suggesting a significant prevalence of 25(OH)D deficiency.4 Similarly, an investigation in Asia reported a 76.8% deficiency rate, indicating that various factors can impact 25(OH)D levels. These include age, gender, skin colour, geography, altitude, diseases, diet, sunscreen use, clothing choices, religious practices and economic development.13

In Africa, a study across seven countries found a 59.4% 25(OH)D deficiency rate. The highest prevalence was observed in northern and South Africa, with women, newborns and urban residents having the lowest 25(OH)D concentrations. Urban populations had less 25(OH)D than rural areas, while traditional lifestyles, such as nomadic animal rearing and hunting, showed the highest 25(OH)D concentrations.14

Ecuadorian studies also found high rates of 25(OH)D deficiency, with 70% of participants in Guayaquil lacking 25(OH)D and 76% of adults in Quito being deficient.15 16 Among 2374 elderly participants in urban and rural areas of Ecuador, 67.8% had low 25(OH)D levels.17

However, defining vitamin D deficiency or insufficiency remains controversial due to varying criteria. The US Institute of Medicine considers a level of <12–20 ng/mL as insufficient and ≥20 ng/mL as sufficient. The Scientific Advisory Committee on Nutrition, on the other hand, considers a level of <12 ng/mL as deficient. It is crucial to exercise caution when selecting cut-off points to avoid overestimating deficiency prevalence. It is also important to acknowledge the ongoing scientific discourse on these cut-off points and their health implications.3

Ecuador, situated in the tropical zone, is longitudinally crossed by the Andes Mountain range, which imparts distinct and prominent topographical characteristics throughout the country. The altitude of Ecuador’s regions holds a significant influence over various health outcomes experienced by its population.16 Within the scope of this study, a pronounced disparity in low 25(OH)D levels was observed in laboratory results obtained from individuals residing in Quito, positioned at an approximate elevation of 2850 masl, in comparison to samples collected from individuals in Santo Domingo, situated at a lower altitude of approximately 625 masl. On comparing participants from Quito, Ambato and Ibarra with those from Santo Domingo, it was found that 69.3% of individuals from higher-altitude cities exhibited low 25(OH)D levels, whereas the percentage was 58.7% among those from Santo Domingo. These findings indicate a potential correlation between altitude and 25(OH)D status, suggesting that individuals inhabiting higher altitudes are more susceptible to insufficient levels of this nutrient. Therefore, it is crucial to consider regional factors when evaluating 25(OH)D status and devising appropriate interventions. Research conducted in Asia by Jiang et al 13 found that people living at lower altitudes (≤500 m) tend to have higher 25(OH)D levels compared with those at higher altitudes (>500 m). Furthermore, it has been observed that low economic status in high-altitude regions might restrict the availability of vitamin D supplements.13 Similarly, studies conducted in South America have incorporated two fundamental factors—altitude and diet—into their analyses. At higher altitudes, the atmosphere is thinner, which results in reduced absorption of ultraviolet radiation and greater production of 25(OH)D(UV levels that increase by 10% to 12% with each 1000-metre increase in altitude).5 18 19 Maybe, this contradictory statement explains that the varying altitudes also influence temperature conditions; for instance, the average temperature in Quito is 13°C, while in Santo Domingo, it’s 25°C.20 Temperature dictates outdoor and indoor activities, with optimal 25(OH)D levels at higher temperatures. However, temperatures exceeding 30°C also show deficiencies; several studies associate extreme temperatures with vitamin D deficits.19 Lifestyle factors such as spending more time indoors for work, leisure and physical activities, coupled with dietary patterns and public health campaigns that promote sunlight avoidance and skin protection, likely contribute to the lower-than-expected 25(OH)D concentrations in this region.5

The findings from the study indicate a high prevalence of low 25(OH)D levels before and during the pandemic. While there was a slight trend towards an increase in monthly average values, the COVID-19 pandemic did not significantly alter this trend. This contrasts with other countries where 25(OHD concentrations were affected by lockdown measures during the pandemic.21 Several studies conducted in countries with distinct seasons also analysed this post-pandemic effect seasonally, highlighting the variability of prevalence rates according to geographical region, environmental conditions, and patient population characteristics. Furthermore, the use of masks during the pandemic may have impacted 25(OH)D levels by reducing the body surface area exposed to solar UVB. Due to restrictions, individuals may not have had sufficient exposure to sunlight, potentially resulting in a decline in 25(OH)D levels. Policies of various countries to supplement the population with vitamin D were also influenced by these factors.21 22

The findings of this study revealed an important prevalence of low 25(OH)D levels in the population, while the incidence of high 25(OH)D was relatively low (0.6%). Interestingly, divergent changes were observed in these indicators during the study period. Although low 25(OH)D levels showed a non-significant reduction and no discernible change in the monthly average of 25(OH)D concentration before the pandemic, there was a notable increase in the prevalence of high 25(OH)D levels from 2018 to 2021. In 2021, the increase in high 25(OH)D levels was significantly greater than in previous years. These findings highlight a concerning pattern in the 25(OH)D levels of the population. These findings are consistent with a study conducted in Ireland that aimed to investigate the impact of the COVID-19 pandemic on 25(OH)D status and the usage of newly introduced vitamin D supplements. A trend analysis based on laboratory data revealed a threefold rise in the yearly average of 25(OH)D during the initial year of the pandemic, compared with two prior trend analyses dating back to 1993 and 2016. The mean 25(OH)D was 2.8 nmol/L higher in the group analysed for the year during the COVID-19 pandemic threefold (61.4, 95% CI 61.5 to 61.7 vs 58.6, 95% CI 58.4 to 58.9, p<0.001). This trend suggests potential benefits for individuals with low vitamin D status but also highlights the risk for those with already high levels, especially considering the increasing availability of high-dose supplements.6

However, it is important to acknowledge the limitations of this study. Important factors such as skin pigmentation, socioeconomic conditions, diet, sun exposure habits, people who were receiving supplements, cultural practices and skin coverage with clothing were not considered in the analysis.4 These factors can influence 25(OH)D levels and should be considered in future research.

The increased consumption of vitamin D supplements by the general population, including therapeutic and high-dose formulations, without adequate medical supervision, can significantly elevate the risk of exogenous hypervitaminosis D, commonly known as vitamin D toxicity. This condition can manifest symptoms of hypercalcemia.23 Therefore, it is essential to ensure that the intake of vitamin D is monitored by healthcare professionals to prevent overdosing and the associated severe health consequences.3 24 25

Excessive intake of vitamin D can lead to the accumulation of the nutrient in the body for extended periods, up to 18 months, resulting in chronic toxic effects such as nephrocalcinosis, hypercalcemia and hypercalciuria. In the past, fortification of foods, such as milk, was recommended as a public health strategy to prevent vitamin D deficiency. However, cases of increased hypercalcemia associated with excessive intake of fortified foods have been reported.3 24 25

During the pandemic, there was a notable interest in studying the relationship between 25(OH)D levels and COVID-19. A study aimed at identifying if online search interest in vitamin D increased with the pandemic burden and analysing the accuracy of public health messaging regarding vitamin D in online news articles found that many articles provided conflicting information or incorrectly advised supratherapeutic doses. This study emphasises the opportunity for public health organisations to capitalise on the increased interest in vitamin D during the pandemic and disseminate accurate information to raise awareness.26

The results of this study reveal a high prevalence of low 25(OH)D levels, indicating the need for strategies to prevent deficiency. However, the increase in high 25(OH)D also raises concerns and highlights the importance of rational prescribing of vitamin D supplements and educating the population to avoid self-medication. To optimise resource allocation and prioritise those at higher risk, it may be beneficial to focus vitamin D testing on specific populations. Individuals with malabsorption syndromes, undergoing steroid therapy or older adults who are confined to their homes are examples of higher-risk groups. Assessing serum of 25(OH)D levels in these cases can provide valuable clinical insights and inform appropriate interventions.