On 2015 Jan 15, William Grant commented:

Vitamin D may explain some of the effect of night shift work and risk of diabetes among African-American women

The paper by Vimalananda and colleagues found that "Long duration of shift work was associated with an increased risk of type 2 diabetes. The association was only partially explained by lifestyle factors and BMI. A better understanding of the mechanisms by which shift work may affect the risk of diabetes is needed in view of the high prevalence of shift work among workers in the USA." [1] In this comment, I outline the evidence that low 25-hydroxyvitamin D [25(OH)D] concentrations due to sleeping during daytime may explain some of the observed effect.

There is evidence from observational studies that low 25(OH)D concentrations are associated with increased risk of diabetes mellitus type 2 [2]. The mechanisms that may explain how vitamin D reduces risk include effects on pancreatic beta cell dysfunction, impaired insulin action and systemic inflammation [3].

Solar UVB exposure is the largest contributing factor to vitamin D production. Those with darker skin produce vitamin D from UVB exposure less efficiently than those with pale skin. As a result, black Americans have significantly lower mean 25(OH)D concentrations than white Americans [4]. This difference has been cited as an important reason for black-white health disparities in the United States [5]. The effect of shift work on risk of diabetes was also discussed in a recent letter to the editor [6].

Thus, raising 25(OH)D concentrations to above 75-100 nmol/L (30-40 ng/mL) may reduce the risk of developing diabetes mellitus type 2 [2] as well as many other adverse health outcomes [8].

References 1. Vimalananda VG, Palmer JR, Gerlovin H, Wise LA, Rosenzweig JL, Rosenberg L, Ruiz Narváez EA. Night-shift work and incident diabetes among African-American women. Diabetologia. 2015 Jan 14. [Epub ahead of print] 2. Song Y, Wang L, Pittas AG, Del Gobbo LC, Zhang C, Manson JE, Hu FB. Blood 25-hydroxy vitamin D levels and incident type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 2013;36(5):1422-8. 3. Mitri J, Pittas AG. Vitamin D and diabetes. Endocrinol Metab Clin North Am. 2014;43(1):205-32. 4. Ginde AA, Liu MC, Camargo CA Jr. Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Arch Intern Med. 2009;169(6):626-32. 5. Grant WB, Peiris AN. Possible role of serum 25-hydroxyvitamin D in Black–White health disparities in the United States. J Am Med Directors Assoc. 2010;11(9):617-28. 6. Grant WB. Low vitamin D concentrations may contribute to the increased risk of diabetes mellitus related to shift work. Occupat Environ Med. 2015;72:161. 8. Pludowski P, Holick MF, Pilz S, Wagner CL, Hollis BW, Grant WB, Shoenfeld Y, Lerchbaum E, Llewellyn DJ, Kienreich K, Soni M. Vitamin D effects on musculoskeletal health, immunity, autoimmunity, cardiovascular disease, cancer, fertility, pregnancy, dementia and mortality- a review of recent evidence. Autoimmun Rev. 2013;12(10):976-89.

Disclosure I receive funding from Bio-Tech Pharmacal (Fayetteville, AR) and MediSun Technology (Highland Park, IL).

On 2015 Jan 15, William Grant commented:

Vitamin D may explain some of the effect of night shift work and risk of diabetes among African-American women

The paper by Vimalananda and colleagues found that "Long duration of shift work was associated with an increased risk of type 2 diabetes. The association was only partially explained by lifestyle factors and BMI. A better understanding of the mechanisms by which shift work may affect the risk of diabetes is needed in view of the high prevalence of shift work among workers in the USA." [1] In this comment, I outline the evidence that low 25-hydroxyvitamin D [25(OH)D] concentrations due to sleeping during daytime may explain some of the observed effect.

There is evidence from observational studies that low 25(OH)D concentrations are associated with increased risk of diabetes mellitus type 2 [2]. The mechanisms that may explain how vitamin D reduces risk include effects on pancreatic beta cell dysfunction, impaired insulin action and systemic inflammation [3].

Solar UVB exposure is the largest contributing factor to vitamin D production. Those with darker skin produce vitamin D from UVB exposure less efficiently than those with pale skin. As a result, black Americans have significantly lower mean 25(OH)D concentrations than white Americans [4]. This difference has been cited as an important reason for black-white health disparities in the United States [5]. The effect of shift work on risk of diabetes was also discussed in a recent letter to the editor [6].

Thus, raising 25(OH)D concentrations to above 75-100 nmol/L (30-40 ng/mL) may reduce the risk of developing diabetes mellitus type 2 [2] as well as many other adverse health outcomes [8].

References 1. Vimalananda VG, Palmer JR, Gerlovin H, Wise LA, Rosenzweig JL, Rosenberg L, Ruiz Narváez EA. Night-shift work and incident diabetes among African-American women. Diabetologia. 2015 Jan 14. [Epub ahead of print] 2. Song Y, Wang L, Pittas AG, Del Gobbo LC, Zhang C, Manson JE, Hu FB. Blood 25-hydroxy vitamin D levels and incident type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 2013;36(5):1422-8. 3. Mitri J, Pittas AG. Vitamin D and diabetes. Endocrinol Metab Clin North Am. 2014;43(1):205-32. 4. Ginde AA, Liu MC, Camargo CA Jr. Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Arch Intern Med. 2009;169(6):626-32. 5. Grant WB, Peiris AN. Possible role of serum 25-hydroxyvitamin D in Black–White health disparities in the United States. J Am Med Directors Assoc. 2010;11(9):617-28. 6. Grant WB. Low vitamin D concentrations may contribute to the increased risk of diabetes mellitus related to shift work. Occupat Environ Med. 2015;72:161. 8. Pludowski P, Holick MF, Pilz S, Wagner CL, Hollis BW, Grant WB, Shoenfeld Y, Lerchbaum E, Llewellyn DJ, Kienreich K, Soni M. Vitamin D effects on musculoskeletal health, immunity, autoimmunity, cardiovascular disease, cancer, fertility, pregnancy, dementia and mortality- a review of recent evidence. Autoimmun Rev. 2013;12(10):976-89.

Disclosure I receive funding from Bio-Tech Pharmacal (Fayetteville, AR) and MediSun Technology (Highland Park, IL).