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Lung Cancer Survival: Vitamin D Could Be Just a Marker of Physical Fitness

Algemeen Ziekenhuis Sint Jan, Brugge, Belgium

To the Editor:

Zhou et al¹ report a positive correlation between circulating 25-hydroxyvitamin D levels and survival in early-stage non–small-cell lung cancer patients. They refer to epidemiologic data and in vitro and animal experiments suggesting that vitamin D has antiproliferative, antimetastasis, and antiangiogenesis activities. However, association does not mean causality, and vitamin D could be just a marker of physical fitness. Sunlight and time of exposure outdoors, determinants of vitamin D levels, are dependent on physical fitness. The correlations between outdoor walking and fitness,² between physical activity and vitamin D levels,³ and among physical fitness, strength, and vitamin D levels^4-6 have been documented in the literature. Physical fitness (as indicated by maximum oxygen concentration (VO₂ max), patient questionnaires, performance scores, or comorbidity scores) is a well-known prognostic variable throughout all stages of lung cancer.^7-10 Physical fitness does not increase with oral vitamin D administration.¹¹ Fitness is also associated with a reduction in all-cause mortality and of cancer-related mortality, especially in men,^12,13 and is associated with a better prognosis in head and neck cancer.¹⁴ The hazard ratios and P values indicated by Zhou et al¹ are more convincing for overall survival than for recurrence-free survival, and that could argue against an effect on tumor biology. Unfortunately, Zhou et al were not able to collect data on outdoor exposure; if they have data on VO₂ max or other indicators of physical fitness, they could investigate whether patients with similar fitness still have a prognosis related to vitamin D levels. They did not intend their article to be read as an incentive for prescribing vitamin D in cancer patients.

AUTHOR'S DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

The author(s) indicated no potential conflicts of interest.

REFERENCES

1. Zhou W, Heist RS, Liu G, et al: Circulating 25-hydroxyvitamin D levels predict survival in early-stage non–small-cell lung cancer patients. J Clin Oncol 25:479-485, 2007[Abstract/Free Full Text]

2. Wong CH, Wong SF, Pang WS, et al: Habitual walking and its correlation to better physical function: Implications for prevention of physical disability in older persons. J Gerontol A Biol Sci Med Sci 58:555-560, 2003[Medline]

3. Scragg R, Holdaway I, Singh V, et al: Serum 25-hydroxyvitamin D3 is related to physical activity and ethnicity but not obesity in a multicultural workforce. Aust N Z J Med 25:218-223, 1995[Medline]

4. Bischoff-Ferrari HA, Dietrich T, Orav EJ, et al: Higher 25-hydroxyvitamin D concentrations are associated with better lower-extremity function in both active and inactive persons aged > or =60 y. Am J Clin Nutr 80:752-758, 2004[Abstract/Free Full Text]

5. Zamboni M, Zoico E, Tosoni P, et al: Relation between vitamin D, physical performance, and disability in elderly persons. J Gerontol A Biol Sci Med Sci 57:M7-M11, 2002[Abstract/Free Full Text]

6. Houston DK, Cesari M, Ferrucci L, et al: Association between vitamin D status and physical performance: The InCHIANTI study. J Gerontol A Biol Sci Med Sci 62:440-446, 2007[Abstract/Free Full Text]

7. Stanley KE: Prognostic factors for survival in patients with inoperable lung cancer. J Natl Cancer Inst 65:25-32, 1980[Medline]

8. Blagden SP, Charman SC, Sharples LD, et al: Performance status score: Do patients and their oncologists agree? Br J Cancer 89:1022-1027, 2003[CrossRef][Medline]

9. Firat S, Bousamra M, Gore E, et al: Comorbidity and KPS are independent prognostic factors in stage I non-small-cell lung cancer. Int J Radiat Oncol Biol Phys 52:1047-1057, 2002[CrossRef][Medline]

10. Firat S, Byhardt RW, Gore E: Comorbidity and Karnofsky performance score are independent prognostic factors in stage III non-small-cell lung cancer: An institutional analysis of patients treated on four RTOG studies—Radiation Therapy Oncology Group. Int J Radiat Oncol Biol Phys 54:357-364, 2002[CrossRef][Medline]

11. Latham NK, Anderson CS, Reid IR. Effects of vitamin D supplementation on strength, physical performance, and falls in older persons: A systematic review. J Am Geriatr Soc 51:1219-1226, 2003

12. Sawada SS, Muto T, Tanaka H, et al: Cardiorespiratory fitness and cancer mortality in Japanese men: A prospective study. Med Sci Sports Exerc 35:1546-1550, 2003

13. Evenson KR, Stevens J, Cai J, et al: The effect of cardiorespiratory fitness and obesity on cancer mortality in women and men. Med Sci Sports Exerc 35:270-277, 2003

14. Jones AS, Fenton JE, Husband DJ: Performance data and survival in head and neck cancer. Clin Otolaryngol Allied Sci 25:396-403, 2000[CrossRef][Medline]

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