Vitamin C & cataracts

[ofonorow]

http://www.wwlp.com/dpp/health/dietitian/nancy-dell-vitamin-c--cataracts-vitamin-d--cholesterol

Most studies, but not all, suggest that Vitamin C from supplements helps prevent cataracts if taken for at least 10 years. One study of older women in Boston who took Vitamin C showed approximately 80% lower prevalence of cataracts compared to women who did not use Vitamin C supplements.

A second study showed a 45% decrease in cataracts with Vitamin C. However, no benefit was seen among those who consumed Vitamin C supplements for less than 10 years.

[Dolev]

Unfortunately, the same study showed a serious increase in cataracts when taking larger doses.

[ofonorow]

Unfortunately, the same study showed a serious increase in cataracts when taking larger doses.

Do you have a link? THx

[Dolev]

Actually it's quoted in that link:

You only need about 150 to 250 mg of Vitamin C per day to saturated the eye. In fact, higher doses may be a problem. A study of women in Sweden taking approximately 1,000 mg of Vitamin C daily for 10 years found a 45% increase in cataract removals compared to those who did not take Vitamin C.

Sure, like I'll stop taking vitamin C cause I believe that cataract "fact".

[majkinetor]

Actually, there might be something to it. Lots of in-vitro studies and several in-vivo studies including the one reported. Might be problem for people that overexpress SVCT2 transporters in the eye.

Vitamin C mediates chemical aging of lens crystallins by the Maillard reaction in a humanized mouse model
http://www.ncbi.nlm.nih.gov/pubmed/17075057



Here is the full study about women and cataractas
http://www.ncbi.nlm.nih.gov/pubmed/19923367

I suppose that this is contextual. For instance glutathion depletion in the eye or some other enzyme related to recycling of DHAA to AA. The risk seem small enough anyway (non significant as reported by authors) and studies are also conflicting.


Also:

Our outcome was cataract extraction instead of cataract diagnosis because of the lack of standardized eye examinations in the entire cohort and incomplete information on cataract status from medical records. We cannot, therefore, exclude the possibility of misclassification of outcome as lens opacities can exist without symptoms; this would draw the risk estimates toward no asso-ciation.
...
However, the exact dose of ascorbic acid in sup-plements was unknown.

But I agree that vitamin C proven positives by far exceed potential negatives.

[ofonorow]

Actually it's quoted in that link:

You only need about 150 to 250 mg of Vitamin C per day to saturated the eye. In fact, higher doses may be a problem. A study of women in Sweden taking approximately 1,000 mg of Vitamin C daily for 10 years found a 45% increase in cataract removals compared to those who did not take Vitamin C.

Sure, like I'll stop taking vitamin C cause I believe that cataract "fact".

So its not the SAME study... Its the same report..

RE:

Here is the full study about women and cataracts
http://www.ncbi.nlm.nih.gov/pubmed/19923367

This study reminds me of a "hit piece". These studies are very comforting to medical doctors, but have little to do with science. The first thing to notice is that this is not a clinical study. That is, no blood levels were measured, etc. (I would wager that an even stronger correlation could have been made between home microwave ovens and cataracts than vitamin C and cataracts. Or with gym shoes, etc.)

The totality of the data would be important. What other "factors" in the data were ignored? How many people taking vitamin C were also taking statin cholesterol lowering drugs (a known cataract inducer in the presence of the common antibiotic erythromycin? http://www.ncbi.nlm.nih.gov/pubmed/11525705)

My first question upon starting to read the full-text, is what were the results of the entire cohort (38,984 women) versus the 24,593 women they chose to analyze.

That would put to rest the question of whether the population was cherry picked.

The following exclusions were made: 1738 women with diagnosis of cancer (except nonmelanoma skin cancer) before baseline in 1997, 89 women with cataract extraction before 1997, 1788 women who moved away from the geographical study area between 1987 and 15 September 1997, and 1751 women with missing information on supplement use status. To avoid influence from changes in dietary habits and in use of dietary supplements due to prevalent chronic disease, we excluded women who, before baseline, reported or were hospitalized with (identified through inpatient registers) diabetes (n = 1040), high blood pressure (n = 5538), and cardiovascular disorders (n = 2447). After these exclusions, the study cohort included 24,593 women

Hmmm. Look at Table 2 in the full text???
http://www.ajcn.org/content/91/2/487/T2.expansion.html

If I take the raw data and find a percentage - (check my math!) -

878/75524 == 0.011625. those woman NOT taking supplements.

143/9134 == 0.01565 Vitamin C

252/16815 == 0.01498 Multivitamins

1619/109173 == 0.01482 Any supplement

Suggests that NOT taking supplements is the best course of action. Hmmm..

Looking at cataract cases versus people

878/9974== 0.08802 No supplement

143/1225 == 0.11673 Vitamin C

252/2259 == 0.11155 Multi

1619/14619 == 0.011560 Any supplement

The data does not pass the reasonableness test, i.e. that taking NO supplement significantly reduces the risk of cataract. Nothing says the supplements were taking over the ENTIRE period of the study.

If I were writing the paper, the conclusions I might draw are that the vitamin C population is small, and that in all probablity, people who begin to lose their eyesight, do a google and find out that supplements, particularly vitamin C, can help and begin taking supplements.

TABLE 2
Association (with 95% CI) between dietary supplement use and surgical cataract extraction in Swedish women (n = 24,593)1
Dietary supplement use
No supplement use
(n = 9974)
Only vitamin C
(n = 1225)2
Only multivitamins
(n = 2259)3
Any supplement
(n = 14,619)
No. of cases 878 143 252 1,619
Person-years 75,524 9134 16,815 109,173
Age-adjusted HR 1.00 (ref) 1.27 (1.07, 1.52) 1.10 (0.95, 1.26) 1.13 (1.04, 1.23)
Multivariable HR4 1.00 (ref) 1.25 (1.05, 1.50) 1.09 (0.94, 1.25) 1.10 (1.01, 1.20)
Excluding first 5 y5
No. of cases 464 76 131 822
Person-years 74,316 8938 16,448 106,793
Age-adjusted HR 1.00 (ref) 1.34 (1.05, 1.71) 1.12 (0.95, 1.36) 1.12 (0.99, 1.25)
Multivariable HR4 1.00 (ref) 1.32 (1.03, 1.68) 1.12 (0.92, 1.37) 1.08 (0.97, 1.22)
1 HR, hazard ratio (obtained from Cox proportional hazards models); ref, reference.
2 Vitamin C use not in combination with other supplements.
3 Multivitamin use not in combination with other supplements.
4 Adjusted for age (5-y age groups: 52, 53–57, 58–62, 63–67, 68–72, 73–77, or
78 y), waist circumference (,80 or
80 cm), smoking (never; mean
lifetime: 10 or .10 cigarettes/d), alcohol consumption (g/d in quartiles), steroid medication use (yes or no), educational level (,10, 10–12, or .12 y), and
hormone replacement therapy use (never, past, or current).
5 Risk of reversed causality checked by excluding the first 5 y of follow-up.

[scurvyencounters]

Can somebody explain this study design so I can understand it better?

DESIGN:
Our study included 24,593 women aged 49-83 y from the Swedish Mammography Cohort (follow-up from September 1997 to October 2005). We collected information on dietary supplement use and lifestyle factors with the use of a self-administrated questionnaire. Cataract extraction cases were identified by linkage to the cataract extraction registers in the geographical study area.


To me, it sounds like this was not a study with measured dosages, but rather based on collected data of free choice vitamin usage. So why do some people choose to take vitamin C and others do not???

I have read that eye problems are often the first indicator of mercury toxicity. And my experience tells me that mercury toxic people need more vitamin C. Therefore, the study seems to be saying that people who take vitamin C may be more susceptible to eye problems, not due to cause and effect, but rather it is because the population group consuming vitamin C have health problems that are benefited by vitamin C. Its the old "correlation is not causation" factor.

Am I missing something???

Ron

[majkinetor]

As always, epidemiology studies can not determine what is cause and what is effect. Thats why they always serve only as a guidance where to put attention for serous scientific clarification.

[ofonorow]

Can somebody explain this study design so I can understand it better?

DESIGN:
Our study included 24,593 women aged 49-83 y from the Swedish Mammography Cohort (follow-up from September 1997 to October 2005). We collected information on dietary supplement use and lifestyle factors with the use of a self-administrated questionnaire. Cataract extraction cases were identified by linkage to the cataract extraction registers in the geographical study area.


To me, it sounds like this was not a study with measured dosages, but rather based on collected data of free choice vitamin usage. So why do some people choose to take vitamin C and others do not???

I have read that eye problems are often the first indicator of mercury toxicity. And my experience tells me that mercury toxic people need more vitamin C. Therefore, the study seems to be saying that people who take vitamin C may be more susceptible to eye problems, not due to cause and effect, but rather it is because the population group consuming vitamin C have health problems that are benefited by vitamin C. Its the old "correlation is not causation" factor.

Am I missing something???

Ron

Nope. I think you hit the nail on the head. All they have shown is that people who get cataracts at some point are likely to try vitamin C.

[Dolev]

in all probablity, people who begin to lose their eyesight, do a google and find out that supplements, particularly vitamin C, can help and begin taking supplements

Right on!