Repost of an email I send out months back explaining why I don't wear sunscreen.

First, some background:
Estimated new cases and deaths from melanoma in the United States in 2009:

New cases: 68,720
Deaths: 8,650

Estimated new cases and deaths from colon and rectal cancer in the United States in 2009:

New cases: 106,100 (colon); 40,870 (rectal)
Deaths: 49,920 (colon and rectal combined)

So we're looking at almost 6X the mortality rate from colorectal cancer alone vs melanoma (not even looking at other cancers that may be modified by Vit D status).

Photochem Photobiol. 2005 Nov-Dec;81(6):1276-86.
Comparisons of estimated economic burdens due to insufficient solar ultraviolet irradiance and vitamin D and excess solar UV irradiance for the United States.
Grant WB, Garland CF, Holick MF.
Sunlight, Nutrition and Health Research Center (SUNARC), 2107 Van Ness Avenue, Suite 403B, San Francisco, CA 94109-2529, USA. [email protected]
Abstract
Vitamin D sufficiency is required for optimal health, and solar ultraviolet B (UVB) irradiance is an important source of vitamin D. UVB and/or vitamin D have been found in observational studies to be associated with reduced risk for over a dozen forms of cancer, multiple sclerosis, osteoporotic fractures, and several other diseases. On the other hand, excess UV irradiance is associated with adverse health outcomes such as cataracts, melanoma, and nonmelanoma skin cancer. Ecologic analyses are used to estimate the fraction of cancer mortality, multiple sclerosis prevalence, and cataract formation that can be prevented or delayed. Estimates from the literature are used for other diseases attributed to excess UV irradiation, additional cancer estimates, and osteoporotic fractures. These results are used to estimate the economic burdens of insufficient UVB irradiation and vitamin D insufficiency as well as excess UV irradiation in the United States for these diseases and conditions. We estimate that 50,000-63,000 individuals in the United States and 19,000-25,000 in the UK die prematurely from cancer annually due to insufficient vitamin D. The U.S. economic burden due to vitamin D insufficiency from inadequate exposure to solar UVB irradiance, diet, and supplements was estimated at $40-56 billion in 2004, whereas the economic burden for excess UV irradiance was estimated at $6-7 billion. These results suggest that increased vitamin D through UVB irradiance, fortification of food, and supplementation could reduce the health care burden in the United States, UK, and elsewhere. Further research is required to confirm these estimates.
PMID: 16159309 [PubMed — indexed for MEDLINE]

Cancer Res. 2007;174:225-34.
An estimate of cancer mortality rate reductions in Europe and the US with 1,000 IU of oral vitamin D per day.
Grant WB, Garland CF, Gorham ED.
Sunlight, Nutrition and Health Research Center, San Francisco, CA 94109-2510, USA.
Abstract
Solar ultraviolet B (UVB) irradiance and/or vitamin D have been found inversely correlated with incidence, mortality, and/or survival rates for breast, colorectal, ovarian, and prostate cancer and Hodgkin's and non-Hodgkin's lymphoma. Evidence is emerging that more than 17 different types of cancer are likely to be vitamin D-sensitive. A recent meta-analysis concluded that 1,000 IU of oral vitamin D per day is associated with a 50% reduction in colorectal cancer incidence. Using this value, as well as the findings in a multifactorial ecologic study of cancer mortality rates in the US, estimates for reductions in risk of vitamin D-sensitive cancer mortality rates were made for 1,000 IU/day. These estimates, along with annual average serum 25-hydroxyvitamin D levels, were used to estimate the reduction in cancer mortality rates in several Western European and North American countries that would result from intake of 1,000 IU/day of vitamin D. It was estimated that reductions could be 7% for males and 9% for females in the US and 14% for males and 20% for females in Western European countries below 59 degrees. It is proposed that increased fortification of food and increased availability of supplements could help increase vitamin D intake and could augment small increases in production of vitamin D from solar UVB irradiance. Providing 1,000 IU of vitamin D per day for all adult Americans would cost about $1 billion; the expected benefits for cancer would be in the range of $16-25 billion in addition to other health benefits of vitamin D.
PMID: 17302200 [PubMed — indexed for MEDLINE]

J Steroid Biochem Mol Biol. 2005 Oct;97(1-2):179-94. Epub 2005 Oct 19.
Vitamin D and prevention of colorectal cancer.
Gorham ED, Garland CF, Garland FC, Grant WB, Mohr SB, Lipkin M, Newmark HL, Giovannucci E, Wei M, Holick MF.
Naval Health Research Center, San Diego, CA 92186, USA.
Abstract
BACKGROUND: Inadequate photosynthesis or oral intake of Vitamin D are associated with high incidence rates of colorectal cancer, but the dose-response relationship has not been adequately studied. METHODS: Dose-response gradients from observational studies of Vitamin D intake and serum 25-hydroxyvitamin D were plotted as trend lines. The point on each linear trend line corresponding to an odds ratio of 0.50 provided the prediagnostic Vitamin D intake or 25-hydroxyvitamin D concentration associated with 50% lower risk compared to <100IU/day Vitamin D or <13ng/ml serum 25-hydroxyvitamin D. Medians of these values were determined. RESULTS: Overall, individuals with >or=1000IU/day oral Vitamin D (p<0.0001) or >or=33ng/ml (82nmol/l) serum 25-hydroxyvitamin D (p<0.01) had 50% lower incidence of colorectal cancer compared to reference values. CONCLUSIONS: Intake of 1000IU/day of Vitamin D, half the safe upper intake established by the National Academy of Sciences, was associated with 50% lower risk. Serum 25-hydroxyvitamin D of 33ng/ml, which is known to be safe, also was associated with 50% lower risk. Prompt public health action is needed to increase intake of Vitamin D(3) to 1000IU/day, and to raise 25-hydroxyvitamin D by encouraging a modest duration of sunlight exposure.
PMID: 16236494 [PubMed — indexed for MEDLINE]

 1. Anticancer Res. 2009 Sep;29(9):3495-500.
Sun and sun beds: inducers of vitamin D and skin cancer.
Cicarma E, Porojnicu AC, Lagunova Z, Dahlback A, Juzeniene A, Moan J.
Department of Radiation Biology, Rikshospitalet-Radiumhospitalet HF, Oslo,
Norway.

Solar radiation is both the main cause of all types of skin cancer, including
cutaneous malignant melanoma (CMM), and the main source of vitamin D accompanied 
by its beneficial effects. The dilemma lies in that increased sun exposure could 
lead to an increase in skin cancers and yet is necessary for the better prognosis
of internal cancers. Solar radiation varies in intensity and spectral composition
with geographic location and time. Of central interest in the present context is 
that the UVA/UVB ratio can vary. Thus, the UVA/UVB ratio increases with
decreasing solar elevation. The ratio is also larger for most sun beds than that 
in the midday sun, but similar to that in the afternoon sun. This may have large 
health implications, since vitamin D is exclusively generated by UVB, while UVA
and UVB likely play a role in the onset of CMM. Sun and sun beds act similarly:
one quantum of radiation at a given wavelength has the same biological effect,
irrespective of the source from which it comes. The winter levels of vitamin D
are 10 to 100% lower than the summer levels in most populations, but can be
brought up to summer levels by moderate sun bed exposure. Doses of 200 IU of
vitamin D per day are not sufficiently large to maintain a summer vitamin D
status in winter. At high latitudes (>40 degrees) the sun provides no vitamin D
in winter. A number of epidemiological studies, interventional studies, animal
studies and cell experiments show that vitamin D reduces the risk and/or
prognosis of internal cancers. Populations living at high latitudes would
probably benefit from moderately increasing their exposure to UVB to provide a
good vitamin D status.

PMID: 19667143 [PubMed — indexed for MEDLINE]

(Note: The latitude of Albuquerque is 35.084N)

2. Clin J Am Soc Nephrol. 2008 Sep;3(5):1548-54. Epub 2008 Jun 11.
Vitamin D and sunlight: strategies for cancer prevention and other health
benefits.
Holick MF.
Department of Medicine, Section of Endocrinology, Nutrition, and Diabetes,
Vitamin D, Skin and Bone Research Laboratory, Boston University Medical Center,
Boston, Massachusetts, USA. [email protected]

Vitamin D deficiency is a worldwide health problem. The major source of vitamin D
for most humans is sensible sun exposure. Factors that influence cutaneous
vitamin D production include sunscreen use, skin pigmentation, time of day,
season of the year, latitude, and aging. Serum 25-hydroxyvitamin D [25(OH)D] is
the measure for vitamin D status. A total of 100 IU of vitamin D raises blood
level of 25(OH)D by 1 ng/ml. Thus, children and adults who do not receive
adequate vitamin D from sun exposure need at least 1000 IU/d vitamin D. Lack of
sun exposure and vitamin D deficiency have been linked to many serious chronic
diseases, including autoimmune diseases, infectious diseases, cardiovascular
disease, and deadly cancers. It is estimated that there is a 30 to 50% reduction 
in risk for developing colorectal, breast, and prostate cancer by either
increasing vitamin D intake to least 1000 IU/d vitamin D or increasing sun
exposure to raise blood levels of 25(OH)D >30 ng/ml. Most tissues in the body
have a vitamin D receptor. The active form of vitamin D, 1,25-dihydroxyvitamin D,
is made in many different tissues, including colon, prostate, and breast. It is
believed that the local production of 1,25(OH)(2)D may be responsible for the
anticancer benefit of vitamin D. Recent studies suggested that women who are
vitamin D deficient have a 253% increased risk for developing colorectal cancer, 
and women who ingested 1500 mg/d calcium and 1100 IU/d vitamin D(3) for 4 yr
reduced risk for developing cancer by >60%.

PMID: 18550652 [PubMed — indexed for MEDLINE]

3. Am J Epidemiol. 2008 Jun 15;167(12):1421-9. Epub 2008 Apr 17.
Are patients with skin cancer at lower risk of developing colorectal or breast
cancer?
Soerjomataram I, Louwman WJ, Lemmens VE, Coebergh JW, de Vries E.
Department of Public Health, Erasmus MC, Rotterdam, the Netherlands.
Comment in:
    Am J Epidemiol. 2009 Apr 1;169(7):918.

Ultraviolet exposure may reduce the risk of colorectal and breast cancer as the
result of rising vitamin D levels. Because skin cancer is positively related to
sun exposure, the authors hypothesized a lower incidence of breast and colorectal
cancer after skin cancer diagnosis. They analyzed the incidence of colorectal and
breast cancer diagnosed from 1972 to 2002 among 26,916 Netherlands skin cancer
patients (4,089 squamous cell carcinoma (SCC), 19,319 basal cell carcinoma (BCC),
and 3,508 cutaneous malignant melanoma (CMM)). Standardized incidence ratios were
calculated. A markedly decreased risk of colorectal cancer was found for
subgroups supposedly associated with the highest accumulated sun exposure: men
(standardized incidence ratio (SIR) = 0.83, 95% confidence interval (CI): 0.71,
0.97); patients with SCC (SIR = 0.64, 95% CI: 0.43, 0.93); older patients at SCC 
diagnosis (SIR = 0.59, 95% CI: 0.37, 0.88); and patients with a SCC or BCC lesion
on the head and neck area (SIR = 0.59, 95% CI: 0.36, 0.92 for SCC and SIR = 0.78,
95% CI: 0.63, 0.97 for BCC). Patients with CMM exhibited an increased risk of
breast cancer, especially advanced breast cancer (SIR = 2.20, 95% CI: 1.10, 3.94)
and older patients at CMM diagnosis (SIR = 1.87, 95% CI: 1.14, 2.89). Study
results suggest a beneficial effect of continuous sun exposure against colorectal
cancer. The higher risk of breast cancer among CMM patients may be related to
socioeconomic class, both being more common in the affluent group.

PMID: 18424428 [PubMed — indexed for MEDLINE]

4. Curr Opin Clin Nutr Metab Care. 2007 Jan;10(1):6-11.
Vitamin D status and cancer: new insights.
Schwartz GG, Skinner HG.
Departments of Cancer Biology and Epidemiology and Prevention, Wake Forest
University School of Medicine, Winston-Salem, North Carolina 27157, USA.

PURPOSE OF REVIEW: The aim of this article is to describe recent developments in 
human studies of the role of vitamin D in the etiology and treatment of cancer.
RECENT FINDINGS: Epidemiologic studies over the past year lend additional support
for important roles for vitamin D in the natural history of several cancers.
Studies showing risk reduction by vitamin D in prostate, colon and breast cancers
were joined by new analyses of endometrial, skin, and pancreatic cancers.
Interest in vitamin D has extended to examinations of its influence on
premalignant conditions such as adenomatous polyps and breast density. Studies of
vitamin D and cancer survival have featured prominently in the recent literature.
Sun exposure and indicators of high vitamin D status were found to be associated 
with improved survival for cutaneous melanoma, Hodgkin's lymphoma, and cancers of
the lung, breast, prostate and colon. Therapeutic trials of vitamin D are
especially prominent in the treatment of prostate cancer. SUMMARY: Studies over
the past year indicate potentially important roles for vitamin D in cancer
prevention, survival and treatment.

PMID: 17143048 [PubMed — indexed for MEDLINE]

5. J Natl Cancer Inst. 2005 Feb 2;97(3):195-9.
Sun exposure and mortality from melanoma.
Berwick M, Armstrong BK, Ben-Porat L, Fine J, Kricker A, Eberle C, Barnhill R.
University of New Mexico, Department of Internal Medicine, New Mexico Cancer
Research Facility, MSC08 4630, Room 103A, 1 University of New Mexico,
Albuquerque, NM 87131, USA. [email protected]
Comment in:
    J Natl Cancer Inst. 2005 Aug 3;97(15):1159; author reply 1159-60.
    J Natl Cancer Inst. 2005 Aug 3;97(15):1158; author reply 1159-62.
    J Natl Cancer Inst. 2005 Feb 2;97(3):161-3.
    J Natl Cancer Inst. 2005 Aug 3;97(15):1158-9; author reply 1159-60.
    J Natl Cancer Inst. 2005 Dec 7;97(23):1789-90; author reply 1791.

BACKGROUND: Melanoma incidence and survival are positively associated, both
geographically and temporally. Solar elastosis, a histologic indicator of
cutaneous sun damage, has also been positively associated with melanoma survival.
Although these observations raise the possibility that sun exposure increases
melanoma survival, they could be explained by an association between incidence
and early detection of melanoma. We therefore evaluated the association between
measures of skin screening and death from cutaneous melanoma. METHODS: Case
subjects (n = 528) from a population-based study of cutaneous melanoma were
followed for an average of more than 5 years. Data, including measures of
intermittent sun exposure, perceived awareness of the skin, skin self-screening, 
and physician screening, were collected during in-person interviews and review of
histopathology and histologic parameters (i.e., solar elastosis, Breslow
thickness, and mitoses) for all of the lesions. Competing risk models were used
to compute risk of death (hazard ratios [HRs], with 95% confidence intervals
[CIs]) from melanoma. All statistical tests were two-sided. RESULTS: Sunburn,
high intermittent sun exposure, skin awareness histories, and solar elastosis
were statistically significantly inversely associated with death from melanoma.
Melanoma thickness, mitoses, ulceration, and anatomic location on the head and
neck were statistically significantly positively associated with melanoma death. 
In a multivariable competing risk analysis, skin awareness (with versus without, 
HR = 0.5, 95% CI = 0.3 to 0.9, P = .022) and solar elastosis (present versus
absent, HR = 0.4, 95% CI = 0.2 to 0.8, P = .009) were strongly and independently 
associated with melanoma death after adjusting for Breslow thickness, mitotic
index, and head and neck location, which were also independently associated with 
death. CONCLUSIONS: Sun exposure is associated with increased survival from
melanoma.

PMID: 15687362 [PubMed — indexed for MEDLINE]

6. Br J Dermatol. 2002 Apr;146 Suppl 61:24-30.
Cutaneous malignant melanoma, sun exposure, and sunscreen use: epidemiological
evidence.
Bastuji-Garin S, Diepgen TL.
Public Health Department, Paris XII University, Henri-Mondor Hospital, 51 avenue 
du Maréchal de Lattre de Tassigny, 94000 Créteil, France.

BACKGROUND: Cutaneous malignant melanoma is the most serious form of skin cancer 
and accounts for about three-quarters of all skin cancer deaths. Over the last
few decades the incidence and mortality rates of melanoma have been increasing
worldwide. The risk of melanoma is higher in individuals with both phenotypic
susceptibility and a history of sun exposure. Therefore, recommended sun
protection behaviours include wearing long-sleeved clothing, seeking shade,
avoiding the sun when it is strongest, and using sunscreen lotion with a sun
protection factor of 15 or higher. It has been reported, however, that the use of
sunscreens does not protect against melanoma and seems to increase the duration
of recreational sun exposure. METHODS: Published epidemiological studies
examining sunscreen use and melanoma have been reviewed from an epidemiological
point of view, taking into account potential biases. We have classified
case-control studies into four categories: (1) inconclusive studies because of
major bias in control population and/or the lack of multivariate analysis; (2) no
association between sunscreen use and melanoma after controlling for confounders;
(3) negative association (i.e. protective effect of sunscreen); and (4) positive 
association. Various other epidemiological studies were also analysed. RESULTS:
These results are controversial. Two case-control studies show a protective
effect of sunscreen use, while three studies showed a significant risk associated
with sunscreen use. However, the discordant results, the low relative risks, the 
lack of dose-effect relationship and the numerous biases, especially the
uncertainty that exposure (sunscreen use) preceded melanoma do not suggest a
causative association between sunscreen use and melanoma. Several hypotheses
could partly explain these contradictory results.

PMID: 11966729 [PubMed — indexed for MEDLINE]

7. Int J Cancer. 1995 Jun 9;61(6):749-55.
Melanoma and use of sunscreens: an Eortc case-control study in Germany, Belgium
and France. The EORTC Melanoma Cooperative Group.
Autier P, Doré JF, Schifflers E, Cesarini JP, Bollaerts A, Koelmel KF, Gefeller
O, Liabeuf A, Lejeune F, Lienard D, et al.

Use of sunscreens is widely advocated as a preventive measure against sun-induced
skin cancers. However, to date, no epidemiologic study has reported a decreased
melanoma risk associated with sunscreen use. We have conducted a case-control
study aimed at evaluating the influence of sunscreen use on the occurrence of
cutaneous malignant melanoma. In 1991 and 1992, 418 melanoma cases and 438
healthy controls were interviewed in Germany, France and Belgium. The
questionnaire used differentiated between regular sunscreens, psoralen sunscreen 
(prepared with 5-methoxypsoralen, a tanning activator and photocarcinogen), and
self-tanning cosmetics (which produce a tan without ultraviolet radiation). After
adjusting for age, sex, hair colour and holiday weeks spent each year in sunny
resorts, the melanoma risk was of 1.50 (95% Cl:1.09-2.06) for regular sunscreens,
and of 2.28 (95% Cl: 1.28-4.04) for psoralen sunscreens. No melanoma risk was
associated with use of self-tanning cosmetics. Among subjects with a poor ability
to tan, psoralen sunscreen users displayed a melanoma risk of 4.45 (95% Cl:
1.25-15.8) when compared with regular sunscreen users. There was a significant
negative interaction between regular sunscreen use and sunburns experienced in
adulthood. Use of sunscreens, especially psoralen sunscreen, was associated with 
higher density of pigmented lesions of the skin. Although we cannot exclude the
presence of an unknown confounding factor, our results support the hypothesis
that sunscreens do not protect against melanoma, probably because of their
ability to delay or avoid sunburn episodes, which may allow prolonged exposure to
unfiltered ultraviolet radiation. Serious doubts are raised regarding the safety 
of sunscreens containing psoralens.

PMID: 7790106 [PubMed — indexed for MEDLINE]

Evidence that the benefits are systemic and not local (not much sun exposure "down there")...

J Photochem Photobiol B. 2010 Mar 12. [Epub ahead of print]
Where the sun does not shine: Is sunshine protective against melanoma of the vulva?
Moan J, Porojnicu AC, Dahlback A, Grant WB, Juzeniene A.
Department of Radiation Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, Montebello, N-0310 Oslo, Norway; Department of Physics, University of Oslo, N-0316 Oslo, Norway.
Abstract
Intermittent sun exposure and sunburn are strong predictors of cutaneous malignant melanoma (CMM). On the other hand, melanomas may arise also in non-sun-exposed areas such as the vulva. However, little is known about a possible relationship between sun exposure and vulvar melanoma. Temporal and latitudinal dependencies of the incidence rates of vulvar melanoma were studied in comparison with those of CMM among Caucasians in Sweden, East Germany, USA and Victoria (Australia). The ratios of vulvar melanoma incidence rates to those of CMM tend to decrease with increasing CMM rates. The incidence rates of CMM have increased with time until recently, while those of vulvar melanoma have either decreased or remain constant. In USA vulvar melanoma incidence rates seem to increase from south to north, while for CMM incidence rates on sun exposed skin areas decrease from south to north. Comparison of latitudinal trends of the incidence rates of vulvar melanomas and CMM show opposite trends. Whenever CMM rates increase, either with time or with decreasing latitude (indicating increased sun exposure) the ratio of vulvar melanoma rates to CMM rates on exposed skin, seem to decrease. Thus, latitudinal trends seem to support the assumption that vulvar melanomas are not generated by UV radiation, and the possibility exists that solar UV radiation, probably via its role in vitamin D photosynthesis in exposed skin, may have a protective effect against vulvar melanoma and should be further investigated. Copyright © 2010 Elsevier B.V. All rights reserved.
PMID: 20359907 [PubMed — as supplied by publisher]