Leonardis vitamin d

Document Sample
Leonardis vitamin d Powered By Docstoc
					Rachel Leonardis

Biology 303

Dr. Ely

November 8, 2007

                           The Delicate Balance of Vitamin D Intake

          In the United States, cancer mortality rates are significantly higher in the

Northeast than in the South. It was long believed that this was due in full to the greater

incidence of factories and pollution in the Northern regions. But as studies of the genetics

behind vitamin D began to circulate in scientific and then popular arenas, this view

shifted. It is now known that exposure to ultraviolet radiation (sunlight) is responsible for

over 90% of the serum 25(OH)D, calcidiol, found in the human body. When this enzyme

is converted by a substrate expressed in many tissues, it becomes 1,25(OH)2, calcitriol,

otherwise known as the most active form of vitamin D. It inhibits invasion of cells and

induces differentiation in concert with the vitamin D receptor (VDR) protein, which is

produced by the VDR gene (1). Because this active hormonal version of vitamin D is

produced in cells of organs prone to so many major cancers (like the breast, colon,

prostate, etc), it seems likely to play a role in the inhibition of the formation and growth

of cancerous cells(6).

          In one report, five studies were encompassed into one statistical analysis

ultimately looking for links between colorectal cancer and vitamin D status in the blood

supply (2). The amount of vitamin D was inferred by directly measuring the amount of
serum 25(OH)D in the blood. Blood samples of 1,448 Caucasian participants were drawn

and divided into five equal groups arranged by serum count. The odds ratios for each

group in terms of cancer incidence was calculated using Peto‟s Assumption Free Method

and compared to the other groups. The results showed an inverse relationship—the higher

the vitamin D level, the lower the cancer incidence. The highest group (with the most

vitamin D present) had approximately a 50% lower incidence of colon cancer than that

observed for the lowest group. Thus, the suggested intake of between 1000 and 2000 IU

of vitamin D daily could help to minimize the risk of colon cancer(2).

       A related study by the same scientists focused on breast cancer‟s link to this

serum 25(OH)D(3). Blood data from 1760 women was pooled from two other large,

reliable studies, the Nurses‟ Health Study and St. George‟s Hospital Study. The results

showed that individuals with approximately 52 nanograms/milliliter of serum 25(OH)D

had a 50% lower incidence of breast cancer in contrast to those women of less than 13

ng/ml of serum. An intake of 2000IU per day in addition to a minimum of 12 minutes of

sunlight per day would generate a serum 25(OH)D level of approximately 52 ng/ml(3).

       In one case-control study of 398 breast cancer patients and 427 control cancer-

free women, three VDR gene polymorphisms were analyzed(4). Two were SNPs that

altered restriction sites for BsmI and FokI, respectively, and the third was a variable-

length Poly(A) sequence. Both the BsmI and the Poly(A) polymorphisms were strongly

associated with breast cancer. The odds of developing breast cancer for a woman with the

BsmI bb genotype or the poly(A) LL genotype was nearly twice that for a woman of BB

or SS genotype (4).
       Another study attempted to relate both aspects of vitamin D and/or UV light

intake in conjunction with the presence of breast cancer by looking at a sample of

Hispanic, African-American, and non-Hispanic White women in the San Francisco Bay

Area from 1995 to 2003(1). There were 1,788 newly diagnosed cases and 2,129 control

women. Measurements were taken initially and after an average time of 14 months had

passed for each individual case, they were taken again. A portable reflectometer was used

to measure skin reflectance from the upper underarm and the forehead in order to

compare natural skin pigmentation with that which is obtained through lifestyle sun

exposure. A significantly decreased risk of breast cancer was observed for those women

with naturally light skin who showed very high sun exposure readings.

       Paradoxically, however, the UVB radiation from sunlight needed to intake

sufficient levels of vitamin D is the same component of sunlight that causes skin cancer.

One study(5) focused on this very topic, asking “Does intermittent sun exposure cause

basal cell carcinoma?” To answer this question, a population-based, case-control study

identified „intermittent exposure‟ as the average weekly time spent in the sun on non-

working days, taking sunburn and extended time periods into account. Basal cell

carcinoma (BCC) refers to the most common type of skin cancer and its risk was seen to

significantly increase with increasing sun exposure. The risk of BCC also substantially

increased more much with those who easily burn than with good tanners. Short, intense

periods of exposure were much more dangerous than the same amount of UVB over a

greater period of time. Such opposing results of vitamin D testing ultimately lead to one

question— where is that delicate balance? How much vitamin D is the right amount? The

United States government‟s current recommended daily intake stands at 400 IU, while
researchers conclude that between 1000 to 2000 IU daily is much more beneficial (7).

Small doses of sunlight (10 to 15 minutes per day) coupled with vitamin D-enriched

foods truly seems to be today‟s best balance of the issue.


1. John, Esther M., Gary G. Schwartz, Jocelyn Koo, Wei Wang, and Sue A. Ingles. 2007.
“Sun Exposure, Vitamin D Receptor Gene Polymorphisms, and Breast Cancer Risk in a
Multiethnic Population.” American Journal of Epidemiology. Advanced access published
on Oct. 12, 2007.

2. Gorham, Garland CF, Garland FC, Grant, Mohr, Lipkin, Newmark, Giovannucci, Wei,
and Holick. 2007. “Optimal vitamin D status for colorectal cancer prevention: a
quantitative meta analysis.” American Journal of Preventive Medicine. 32: 210-216.

3. Gorham, Garland CF, Garland FC, Grant, Mohr, Lipkin, Newmark, Giovannucci, Wei,
and Holick. 2007. “Vitamin D and prevention of breast cancer: pooled analysis.” The
Journal of Steriod Biochemistry and Molecular Biology. 103: 708-711.

4. Guy, M, LC Lowe, D Bretherton-Watt, Mansi, Peckitt, Bliss, Wilson, and Colston.
2004. “Vitamin D receptor gene polymorphisms and breast cancer risk.” Clinical Cancer
Research. 10: 5472-5481.

5. Kricker, A, BK Armstrong, DR English, and PJ Heenan. 1995. “Does intermittent sun
exposure cause basal cell carcinoma? a case-control study in Western Australia”
International Journal of Cancer. 60: 489-494.

6. Weatherby, Craig. 1993-2007. “Vitamin D May Lower Risk of Ovarian, Breast,
Kidney, and Colon Cancers” Health and Beyond Online.

7. Mittelstaedt, Martin. 2007. “Vitamin D casts cancer prevention in new light” Globe
and Mail.

Shared By: