DEAR DR. BLONZ: I have concerns about contaminants in fish oil supplements. Is an omega-3 supplement sourced from flax a better alternative? -- F.L., Phoenix

DEAR F.L.: I recommend eating fish over taking fish-oil supplements. Population studies have shown that those with a regular consumption of fish have a lower risk of several chronic diseases, including heart disease, hypertension and certain inflammatory conditions, such as arthritis.

Your question, however, relates to supplements, so let's consider the issue.

The key components are specific omega-3 fatty acids. Fish containing high levels of these include salmon, mackerel, tuna, herring, anchovies, sardines and trout. There are also omega-3 fatty acids in flaxseed and, to a lesser extent, canola and walnut oils, but these are not the same as those found in fish.

To be called an omega-3 means that the first unsaturated bond is on the third carbon of the chain. In fish, we have omega-3s often referred to by their initials: EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). They are 20 and 24 carbons long, respectively. The omega-3 in flaxseed and other plant sources is linolenic acid, which is 18 carbons long.

Most people need more omega-3 fats in their diet, whether they come from fish or flax, but there are unique benefits in EPA and DHA.

If you do consume the 18-carbon linolenic acid, your body has the ability to elongate some of it into EPA and DHA, but only a small amount makes it through this process. It is, however, better to have omega-3s from flaxseed than to not have any at all.

Plant sources of omega-3 fats are relied upon by vegans. In addition to fish, EPA and DHA can be found in krill (a crustacean) and in some forms of algae; it is up to the individual to decide the boundaries of their vegan eating plan. I would be remiss if I didn't mention that flaxseed has other health attributes: It is an excellent source of dietary fiber and lignan, a phytochemical that may have anti-cancer effects.

As for pollution, this remains a disturbing topic, and some fish populations have been affected by various contaminants. When eating fish, steer clear of those caught or raised near industrial plants, and stick with those from offshore or deep-sea areas, or from lakes and streams known to be free from harmful chemicals. You might seek guidance from a reputable fish market.

Where supplements are concerned, it is best to check individual products to find one that is free of contaminants. There are processes that allow manufacturers to filter out environmental toxins without affecting the level of the omega-3 fatty acids. Look for an appropriate description on the label stating that the product is contaminant-free. If in doubt, give the manufacturer a call.

One final note: Fish oil supplements should be avoided by those with bleeding disorders and those on anticoagulant medications. Caution is also dictated for those with high blood pressure. Always consult your physician if you have any questions.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: What is the story with having a "sluggish liver"? An article I recently read said that symptoms of a sluggish liver can include having a hard time losing weight, experiencing various abdominal pains or even having cellulite. This piqued my interest, and I found more on the topic, with some articles making specific recommendations for herbs and other dietary supplements. Should I try these treatments? -- F.S., Madison, Wisconsin

DEAR F.S.: The entire concept of a "sluggish liver" has no real medical meaning. I have seen the term used to explain everything from hemorrhoids to migraine headaches. It is difficult to answer the specifics of your question, because to do so would justify your conclusion that a "sluggish liver" was the source of your problems. I cannot help but doubt that this is so.

Our liver is very complex: perhaps the hardest-working and most diverse organ in our body. Its responsibilities include: making our blood; manufacturing proteins; detoxifying chemicals, including alcohol and all matter of drugs and contaminants, whether eaten, injected, absorbed through the skin or present in the air we breathe; making and storing glycogen, a form of stored glucose (blood sugar); turning excess calories into fat for storage; burning fats when necessary; creating ketones when there is insufficient glucose in the blood; producing bile, a substance that helps digest food; storing iron and some other vitamins and minerals; and making the factors that help clot the blood.

The obvious implications of this impressive list is that there can be serious consequences if the liver is not functioning up to par. But what does it mean to have a "sluggish liver"? This nonspecific term is unhelpful. It would be similar to proclaiming "something is wrong," and then expecting this singular confession to give rise to specific advice that will make it right.

With problems involving the liver, the first step should be to determine what's going on. To do this, you'll need to see a health professional, who will take a careful history, do a physical examination and order the appropriate laboratory tests.

Depending on what is at play, it is possible that there might be some treatment that can help, but what works for one individual might be counterindicated for another. The bottom line is that you risk making things worse by trying treatments on your own without knowing the source of the problem, and whether the liver is even involved. I encourage you to take the time to get the needed information before you proceed.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Coffee is a part of my morning routine, but I have read that there might be an association between coffee and rheumatoid arthritis. The thought of this is giving me a real headache. I usually have a cup in the morning and another with lunch. My parents both have osteoarthritis, and I certainly don't want to take steps down any road that might lead to that. -- K.D., San Diego

DEAR K.D.: Don't toss your coffee beans yet. There has been research reporting a potential connection between decaf coffee-drinking and the risk of rheumatoid arthritis -- a form of arthritis involving the immune system. This is not the same as osteoarthritis (see tinyurl.com/jga42vh for more on the different forms). The type of research you reacted to was epidemiological, often referred to as a "population study." Such research reports coincidences between the factors it measures, but not causation: It doesn't tell you what, if anything, is causing what.

In this case, the study, in the January 2002 issue of the journal Arthritis and Rheumatism, reported an increased risk of rheumatoid arthritis in women drinking more than four cups of decaffeinated coffee per day. It did not conclude that drinking decaf causes rheumatoid arthritis.

My favorite example of the limits of epidemiological research was a finding that physicians who eat meat and drink alcohol have a significantly lower risk of being killed in a plane crash. So, should all docs have a burger and a beer before every flight? Of course not. But if there is nothing going on, why would this relationship be found? It turns out to be one of the quirks of research involving large amounts of data, and it is the reason we need more than a mere statistical relationship before giving full credence to results.

With the coffee study, for example, there might be other factors that have yet to be considered. Next steps might be replication with other populations to see if the relationship held. If so, there could then be an examination of other variables, such as method of coffee preparation or other dietary and lifestyle factors, that might be at play.

That 2002 study was countered by a subsequent study in the November 2003 issue of the same journal. This one failed to support the relationship between coffee, tea and rheumatoid arthritis. A November 2014 study in the journal Clinical Rheumatology performed a meta-analysis on the relationship between coffee (or tea) consumption and the risk of rheumatoid arthritis. A meta-analysis is one in which multiple studies, all meeting specific criteria, are combined and their data viewed collectively. This study reported there was a relationship between a high coffee consumption (four or more cups per day), and the risk of rheumatoid arthritis -- but only with individuals having a positive blood test for rheumatoid arthritis. For those with a negative test, no relationship was found.

The bottom line is that there is no evidence that drinking coffee raises risk of osteoarthritis (the type your parents have). Coffee has also not been shown to cause rheumatoid arthritis, but for those who already have this condition, there may be a reason to limit consumption. It is certainly something best discussed with your physician or rheumatologist.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.