0
$\begingroup$

A study claims that fish consumption increases the likelihood of getting skin cancer. Since another older study claimed that omega-3 consumption increases the likelihood of prostate cancer is there any evidence that omega-3 is at least partly responsible for the increased likelihood of cancer assuming that the result of the first study is accurate?

$\endgroup$
3
  • $\begingroup$ The study doesn’t mention fish (that I saw on glancing at it) at all. How did you jump to fish? Also, can you support your statement about omega 3 fa? There’s a good chance you missed something. Thanks. $\endgroup$ Commented Jun 15, 2022 at 22:25
  • $\begingroup$ There are academic-ish articles that you could have referenced such as this which suggest a link, but with indeterminate cause as far as I can tell (they guess it's toxin contaminants). $\endgroup$ Commented Jun 15, 2022 at 23:28
  • 1
    $\begingroup$ The summary article states Data showed that the risk for developing SCC and BCC was associated with a higher intake of polyunsaturated fats. While the risks of SCC, BCC, and melanoma were associated with a higher omega-6 fat intake, omega-3 dietary fat intake was found to be associated with risk of BCC but not with SCC or melanoma. No other fats were associated with melanoma risk. $\endgroup$
    – bob1
    Commented Jun 16, 2022 at 4:37

1 Answer 1

4
$\begingroup$

Honestly spoken, I doubt the results of this study and there are a few reasons for this. To start with, we have to recognize that the authors did quite a lot of work to exclude bias and false conclusions. They did their study as a prospective study which means they collected the data first (questionnaire on eating habits) and watched the people afterwards to see the outcome. This avoids wrong conclusions or bias in terms of what has been eaten. Also, the sample size is sufficiently large, which is often problematic in such studies.

To categorize the results: In this study, the effect size was not very strong, the hazard ratio was 1,22 (with a 95% CI = 1.11-1.34 ) meaning a 22% higher risk of developing melanoma. The absolute lifetime risk for developing melanoma in the US for white skinned people is about 2,6%, putting a 22% increase on top would translate in a absolute risk of around 3,2%.

However, some points are to be criticized, some mentioned by the authors. First, this is a study which relies on a self-reported questionnaire on their fish consumption in the year before and then tracked the participants for 15 years. This is not very hard data, since I would probably misjudge the amounts of the different stuff I ate and drank over the course of the lase year. Additionally it does not factor in changes in lifestyle (some people may become vegetarians, I personally ate a lot more fish when I lived close to the sea since it was easily obtainable and so on).

Then there are factors which are a lot more important for developing melanoma. This includes exposure to UV radiation (sun and sun tanning booths), mole count and if you are lightskinned/have red hair. For the later the absolute risk for getting melanoma is about 400% higher than for people with dark hairs. Also the UV exposure: The study did not ask for the personal habits on UV exposure (meaning working outside a lot like gardening or other outdoor activities or using tanning booths), they calculated the UV associated risk by the median UV radiation based on the place of living at the beginning of the study. As far as I can see they did no further correction for places of living for the following 15 years which might have brought a much higher (or lower exposure). Not correcting for these importants factor contributing to the development of melanoma is very problematic and can skew the whole statistic. What happens if the group of "fish related melanoma" contains disproportionately many redhaired people?

Some points are just curious. The authors distinguished between canned tuna, fried and non-fried fish and found a correlation to the development of melanoma only between non-fried fish and canned tuna. This is an observation for which they do not really have an explanation. Additionally the median age in which melanoma where first detected was 70,1 years, according to the American cancer society this age for the whole population is around 65 years of age. This might not be significant but is at least odd.

The authors themselves speculate about some toxins like arsenic, mercury or polychlorinated biphenyls which have been connected to melanoma in recent studies, but fail to explain why this would not cause problems with fried fish.

Taken together, this is a relatively weak link which is not supported by strong indications while there are other, strong causes of disease which have not been analyzed further. If there is such a link, I think this is a very weak and not very important one.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .