102 - Is Sunlight Exposure and Vitamin D Intake Associated with Rheumatoid Arthritis?

Sunday, November 6, 2011: 9:00 AM-6:00 PM
Hall F2 - Poster Hall (McCormick Place West)
Nicole C. Wright1, Brian T. Walitt2, Jeffery R. Curtis1, Mary Pettinger3, Christine G. Parks4, Anneclaire J. De Roos3, Jean Wactawksi-Wende5, Rachel Mackey6, Rebecca D. Jackson7, Michal L. Melamed8 and Barbara V. Howard9, 1University of Alabama at Birmingham, Birmingham, AL, 2Washington Hospital Center, Washington, DC, 3Fred Hutchinson Cancer Research Center, WA, 4NIH/NIEHS, Research Triangle Park, NC, 5University of Buffalo, Buffalo, NY, 6University of Pittsburgh, Pittsburgh, PA, 7Ohio State University, Columbus, OH, 8Albert Einstein College of Medicine, Bronx, NY, 9Medstar Research Institute, Washington, DC
Presentation Number: 102

Background/Purpose: Dietary vitamin D intake has been studied as a risk factor for incidence of RA in several longitudinal cohort studies; however, only few have evaluated sunlight exposure, the primary source of vitamin D, and the risk of RA.

 

Methods: Using the Women's Health Initiative Observational Study (WHI-OS), we examined the association between vitamin D exposure on the prevalence and incidence of rheumatoid arthritis (RA). Prevalent RA cases were identified using the combination of self-report and medications at baseline. Incident cases were ascertained using year three data, and the comparison group consisted of women who did not report RA at either time point. Vitamin D exposure was identified in three ways: 1) vitamin D intake from food frequency questionnaire and supplementation sources, 2) previous sunlight exposure, and 3) current sunlight exposure. Previous sunlight exposure was ascertained via questions regarding time spent outdoors during summer and non-summer months as a child, in their teens, and in their thirties. Respondents answering <30 minutes were given a score of 15; respondents answering 30 minutes to 2 hours were given a score of 75, and those responding ≥2 hours were  given a score of 180. The scores at each period were summed to create cumulative minutes of previous sunlight exposure. Mean solar irradiance, calculated using the clinical center location and national weather data, was used to ascertain current sunlight exposure. The three exposure variables were categorized and after controlling for several variables, the association with prevalent RA was tested using logistic regression and the association with the incidence of RA was tested using Cox-proportional hazards models.

 

Results:  The study population included 76,743 women without RA, 727 prevalent RA cases, and 190 incident RA cases. Women with RA were significantly older, heavier, and had a larger proportion of African Americans and current smokers than the comparison group. After adjustment, no association between vitamin D exposure and the prevalence of RA was found in the total population; however different trends were observed by race (Table). Though not statistically significant in either group, compared to the highest category of summer sunlight exposure (>500 minutes), White women with the lowest exposure (<300 minutes) were 15% less likely to have prevalent RA [OR (95% CI): 0.85 (0.65, 1.10)] whereas African American women in the lowest category were 17% more likely [1.17 (0.60, 2.28)]. Similar differences in racial trends were found in the other exposure variables. No significant association between vitamin D exposure and the incidence of RA was found.

 

Conclusions: Self-reported estimates of lifetime and current vitamin D exposure were not associated with incidence or prevalence of RA in the WHI-OS; however, results suggest that race may modify the association between vitamin D exposure and RA.   

 

Table. The Association between Vitamin D Intake, Sunlight Exposure and the Prevalence of Rheumatoid Arthritis by Race

 

White

 

African American

 

N/# cases

OR (95% CI)*

 

N/# Cases

OR (95% CI)*

Vitamin D Intake (IU/day)

 

 

 

 

 

≥600

<600-400

<400-200

<200

13,674/ 114

15,683/ 143

10,527/ 76

18,440/ 125

1.00

1.08 (0.85, 1.39)

0.85 (0.64, 1.14)

0.75 (0.58, 0.97)

 

358/ 4

849/ 16

589/ 8

2,084/ 35

1.00

1.64 (0.54, 4.96)

1.17 (0.35, 3.91)

1.32 (0.47, 3.75)

Sunlight Exposure summer (mins)

 

 

 

 

 

>500

500-400

400-300

<300

15,028/ 126

17,574/ 143

12,100/ 91

14,124/ 101

1.00

0.95 (0.75, 1.21)

0.89 (0.68, 1.17)

0.85 (0.65, 1.10)

 

1,073/ 17

1,308/ 17

750/ 14

1,030/ 18

1.00

0.87 (0.44, 1.71)

1.22 (0.59, 2.49)

1.17 (0.60, 2.28)

Sunlight Exposure other seasons (mins)

 

 

 

 

 

>400

400-300

300-200

<200

15,722/ 149

8,112/ 58

20,941/ 151

13,888/ 97

1.00

0.78 (0.57, 1.05)

0.81 (0.64, 1.01)

0.76 (0.59, 0.99)

 

1,471/ 23

551/ 11

1,217/ 17

884/ 14

1.00

1.34 (0.65, 2.78)

0.96 (0.51, 1.80)

1.01 (0.52, 1.97)

Solar Irradiance (g-cal/cm2)

 

 

 

 

 

500-475

430-400

380-375

350        

325-300

11,771/ 85

9,550/ 80

6,745/ 50

12,743/ 77

18,935/ 175

1.00

1.18 (0.86, 1.62)

1.05 (0.72, 1.52)

0.80 (0.58, 1.10)

1.28 (0.97, 1.68)

 

404/ 10

959/ 17

1,101/ 12

1,321/ 19

538/ 12

1.00

0.69 (0.31, 1.53)

0.43 (0.18, 1.00)

0.54 (0.25, 1.18)

0.88 (0.38, 2.08)

*Adjusted for age, BMI, region at birth, education, smoking, alcohol, weight at birth wearing hat outdoors during thirties, and total recreational physical activity

 

 


Keywords: environmental factors, nutrition and rheumatoid arthritis (RA)

Disclosure: N. C. Wright, None; B. T. Walitt, Jazz Pharmaceuticals, 5 ; J. R. Curtis, Merck Pharmaceuticals, 5, Amgen, 5, Eli Lilly and Company, 5, Merck Pharmaceuticals, 2, Roche Pharmaceuticals, 5, Novartis Pharmaceutical Corporation, 2, Proctor and Gamble, 2, Novartis Pharmaceutical Corporation, 5, Eli Lilly and Company, 2 ; M. Pettinger, None; C. G. Parks, None; A. J. De Roos, None; J. Wactawksi-Wende, None; R. Mackey, None; R. D. Jackson, None; M. L. Melamed, None; B. V. Howard, None.