Sooyun Christina Kim, Amreet Minhas, Beatrice Sixt
Project Smile Global
January 12, 2025

Seasonal affective disorder (SAD) is a form of recurrent depression, previously defined as a syndrome in which depressive episodes develop during the fall and winter, but is now classified as a type of bipolar disorder or depression known as MDD with Seasonal Patterns (Jahan-Mihan 2). While results remain inconsistent, some evidence supports that dietary nutrients, particularly vitamin D, can alleviate some symptoms of SAD (Jahan-Mihan 15). Concerningly, available data suggests that vitamin D deficiency is widespread and is a re-emerging global health problem (Antonucci et al 1). The prevalence of vitamin D deficiency worldwide has been considered a “pandemic”, with rates continuing to increase (Amrein et al. 1499; Holick & Chen 1080). While numerous factors play a role in the onset of vitamin D deficiency, elements of modern lifestyles such as lack of physical activity and exposure to sunlight, among others, have exacerbated this issue (Cui et al. 2). Having sufficient levels of vitamin D is imperative for bone health, which is essential for prevention of a multitude of health issues, such as cancer and cardiovascular disease. (Cui et al. 2).

In terms of how we acquire vitamin D, the main sources of the vitamin are direct sunlight exposure, supplements, and diet (Dos Santos et al. 2). When light from the sun comes into contact with the surface of the skin, a precursor of vitamin D, 7-dehydrocholesterol, or 7-DHC, is converted to the vitamin in the presence of UVB radiation (Dos Santos et al. 2). This form of the vitamin undergoes structural changes in the liver, and its active form is achieved in the kidneys (Dos Santos et al. 2). As for consuming vitamin D, there are very few foods that naturally contain it (Botelho et al. 1). Fish such as salmon and tuna, as well as some cheeses and dairy products are sources of vitamin D (Holick & Chen 1080). Additionally, milk is often fortified with vitamin D, making it a crucial vitamin source for many (Holick and Chen 1080). Since it may be difficult to obtain vitamin D from the diet, supplements are also readily available. Similar to sunlight exposure, dietary vitamin D is inactive and must undergo the same changes in the liver and kidneys in order to be used by the body (Forrest & Stuhldreher).

Vitamin D plays a significant role in human health on multiple levels, including affecting the proper functioning of musculoskeletal, immune, nervous, and cardiovascular systems (Zmijewski 1). Low levels of vitamin D, also known as hypovitaminosis, are associated with an increased risk of cancer, type 1 diabetes mellitus, cognitive decline, autoimmunity, and depression (Hossein-nezhad and Holick 1). They can also cause a decrease in calcium levels, which leads to inadequate mineralization of bones and teeth, leading to high chances of osteoporosis or bone fractures in both children and adults (Antonucci et al 1). Apart from affecting tooth mineralization, vitamin D deficiency has profound effects on other aspects of oral health, including periodontitis, gingival infection, and increased incidence of caries (Botelho et al 3).
Periodontitis, or gum disease, is a common disease caused by bacteria, often marked by the formation of plaque and chronic inflammation of the gums (Darveau 1). Although not fully understood, vitamin D has anti-inflammatory and mineralization effects on the periodontium, helping prevent or alleviate periodontitis (Botelho et al 6). A cross-sectional study found that periodontitis patients had lower levels of vitamin D and higher levels of inflammation compared to healthy periodontal individuals (Taskan & Gevrek 1). However, the data is conflicting, as some studies have found that vitamin D concentrations were associated with increased periodontal destruction, , accelerating the severity of disease, and higher tooth loss (Dietrich et al 111). It is important to note that intake of vitamin D alone is a poor indicator of serum vitamin D concentrations, as exposure to sunshine is another determinant factor (Dietrich et al 111). Furthermore, without knowing baseline serum vitamin D concentrations, it is impossible to determine the vitamin’s effect on periodontal conditions (Uwitonze et al 7). Most studies support the idea that vitamin D is involved in the pathogenesis of periodontitis, impacting tooth mineral density and therefore reversing the severity of periodontitis (Uwitonze et al 9).
Socioeconomic factors have a notable impact on vitamin D access. They influence diet and environment, which are instrumental in two of the main sources of absorption. During adolescence – when vitamin D is crucial for development – children in low income communities have been found to have lower sun exposure time (Dos Santos et al). This is because these factors significantly impact outdoor play, which is when sunlight can naturally be absorbed. Parents’ perceptions of their neighborhood influence outdoor play , with children who report higher levels of fears or concerns relating to outdoor play having significantly less time outside (Loebach et al). Additionally, poor socioeconomic factors pose barriers to outdoor play through lack of access to safe and appropriate spaces, unsafe neighborhoods and no organized affordable physical activity programs (Chang). Studies have found fewer opportunities for low income mothers and their children to engage in physical activity due to a lack of time and energy from heavy domestic responsibilities and work schedules.
Diet is substantially impacted by low socioeconomic status. Food deserts, which are areas where healthy, high-quality foods are limited, are more prevalent in minority-dominated neighborhoods (Samson). This pushes these communities towards low-nutrition, processed options, like fast food. A study showed that neighborhoods with an 80% or greater proportion of African American residents had an average of 2.4 restaurants/mile2 compared to 1.5 restaurants/mile2 in neighborhoods with only 20% African American residents. Additionally, the price of groceries provides another barrier to accessing vitamin D-rich foods. Increasing grocery prices lead to an increase in obesity levels, suggesting a link between food prices and dietary choices (Drewnowski ).
Along with maintaining the function of various systems in the body, vitamin D sufficiency is crucial for oral health. Low vitamin D levels are associated with a decrease in calcium circulating in the body, compromising the strength of teeth and bones. This can contribute to the development of infections, decay, and fractures. Those with low socioeconomic status face higher rates of vitamin D deficiency due to its impact.
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