SPECIAL EDITION. The Inequity of Vitamin D
With such a positive response to the vitamin D series, it is only prudent to address something we rarely consider in nutrition – the inequity of Vitamin D.
This series has shown how important it is for many bodily functions, including bone health and immune function. Despite this, the fact remains that darker-skinned individuals may be at a disadvantage when it comes to getting enough vitamin D from the sun.
Here's why.
Endogenous vitamin d production (within the body) is dependent on exposure to sunlight. Ultraviolet (UV) rays from the sun interact with a compound in the skin known as 7-dehydrocholesterol, converting it into vitamin D3. Because melanin—the pigment that gives skin its colour—absorbs UV light, it stands to reason that darker-skinned individuals would require more sun exposure to produce the same amount of vitamin D as someone with lighter skin.[1]
This difference in production has real-world implications.
A team out of the University of Manchester found that the recommended summer sun exposure for UK adults failed to produce significant vitamin changes in those of South Asian origin.[2] In fact, the researchers in this study noted,
“Improving the vitamin D status of the skin type V population requires either an oral intervention through food fortification or vitamin D supplements, or a change in behavior to increase the vitamin D synthesized in the skin. Much of the public health guidance available for sun exposure encourages sun protection, taking little account of skin type, while cultural expectations may limit skin exposure.”
A study published in 2022 found that otherwise healthy black and Hispanic teens were more likely than white patients to be diagnosed with vitamin D deficiency. Over 61% of those tested in this study had low levels of the important nutrient.[3] Other research has shown that African American women of childbearing age are more likely to lack this nutrient. This is significant because vitamin D is essential for pregnant women and growing infants—a lack of vitamin D has been linked to complications like preterm birth, growth restriction, and preeclampsia.[4]
More recent evidence even viewed the recent COVID-19 infection as a disease of color because of the “…striking differences within and between populations…”[5] Those most at risk shared a number of risk factors, including darker skin pigmentation and inadequate sun exposure.[6]
When it comes to oral supplementation, the picture is interesting, to say the least. Vitamin D is a known gut microbiota modifier, with oral supplementation increasing the diversity of species found in the digestive tract.[7] Data like this is important considering how the microbiome influences our long-term health. Black Americans have an increased incidence of colorectal cancer and vitamin D can lower this by 50%.[8,9] This makes it a worthwhile intervention for many care providers to consider for the health of their patients.
Additionally, many Black and Hispanic people live in "food deserts"—areas without easy access to foods rich in natural forms of vitamin D like salmon and trout.[10,11] Given all these factors, it's clear that more needs to be done to level the playing field when it comes to getting enough vitamin D—especially for dark-skinned people who are disproportionately affected by deficiency.
References
Webb, Ann R. "Who, what, where and when—influences on cutaneous vitamin D synthesis." Progress in biophysics and molecular biology 92.1 (2006): 17-25.
Farrar, Mark D., et al. "Recommended summer sunlight exposure amounts fail to produce sufficient vitamin D status in UK adults of South Asian origin." The American journal of clinical nutrition 94.5 (2011): 1219-1224.
Varghese, Shainy B., Julia Benoit, and Teresa McIntyre. "Vitamin D Levels in Ethnic Minority Adolescents in Primary Care." Journal of Pediatric Health Care (2022).
Bodnar, Lisa M., and Hyagriv N. Simhan. "Vitamin D may be a link to black-white disparities in adverse birth outcomes." Obstetrical & gynecological survey 65.4 (2010): 273.
Sidiropoulou, Polytimi, et al. "Unraveling the roles of vitamin D status and melanin during Covid‑19." International journal of molecular medicine 47.1 (2021): 92-100.
House, Napier, H. Holborn, and L. Wc. "ICNARC report on COVID-19 in critical care." ICNARC 17 (2020): 1-26.
Singh, Parul, et al. "The potential role of vitamin D supplementation as a gut microbiota modifier in healthy individuals." Scientific reports 10.1 (2020): 1-14.
Mai, Volker, et al. "Associations between dietary habits and body mass index with gut microbiota composition and fecal water genotoxicity: an observational study in African American and Caucasian American volunteers." Nutrition journal 8.1 (2009): 1-10.
Klampfer, Lidija. "Vitamin D and colon cancer." World journal of gastrointestinal oncology 6.11 (2014): 430.
Sansom, Garett, and Bryce Hannibal. "Disparate access to nutritional food; place, race and equity in the United States." BMC nutrition 7.1 (2021): 1-6.
Bower, Kelly M., et al. "The intersection of neighborhood racial segregation, poverty, and urbanicity and its impact on food store availability in the United States." Preventive medicine 58 (2014): 33-39.