In the last few weeks, various news sources published story after story of people who contracted a flesh-eating bacteria called Vibrio vulnificus. This bacteria isn’t just a problem for swimmers — it can also infect people who eat raw and undercooked shellfish, especially oysters. And although the U.S. Centers for Disease Control and Prevention estimates that there are only about 205 cases of V. vulnificus infections in the United States each year, some scientists are already saying that the number could rise due to warming waters from climate change.1
If you’re a seafood lover, these headlines along with the already well-known risks of parasites, heavy metals, and chemicals may have you thinking twice before going to a sushi restaurant for date night. So should you stop eating seafood? The simple answer is no, but read on to find out why the benefits of seafood greatly outweigh the risks, and the steps you can take to continue enjoying seafood this summer.
Mercury in Seafood
Let’s talk about mercury.
Yes, it’s true that mercury — in its organic form, methylmercury (MeHg) — accumulates in fish and other seafood. And, as we all know, methylmercury can be highly dangerous.
At high levels of MeHg exposure, you may experience symptoms of neurotoxicity. A few examples of acute methylmercury poisoning include:
- Numbness or tingling in hands and feet
- Difficulty walking or lack of coordination
- Impairment of peripheral vision, tunnel vision
- Slurred speech and hearing
- Vision changes
- Muscle weakness
While many people are familiar with symptoms of acute exposure to methylmercury, the symptoms of chronic, lower level methylmercury exposure are less well known. The following are symptoms of chronic methylmercury exposure:
- Sleep disturbance
- Heart rate disturbance
- Stomach upset
- Depression, anxiety
- Memory loss
- Difficulty concentrating
- Muscle and joint pain
- Hair thinning
- Impaired coordination
Pregnant women, breastfeeding mothers, and young children are at the greatest risk of experiencing the neurotoxic effects of methylmercury. However, this does not mean that anyone, including those in the “at risk” groups, should eliminate seafood from their diet. In fact, avoiding seafood during pregnancy could backfire due to the deprivation of important nutrients like omega-3 fatty acids.
Therefore, the question is not whether we should eat or not eat seafood. Rather, it is about which type and species of seafood we should eat and the quantities we should consume.
For the “at risk” population, the U.S. Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA) recommend a limit of 8 to 12 ounces of seafood per week from the following list which are lower in methylmercury (less than 0.1 ppm). The asterisk (*) indicates seafood that are higher in the omega-3 fatty acids EPA and DHA:
- Salmon (*)
- Herring (*)
- Sardines (*)
- Anchovies (*)
- Trout (*)
- Canned light tuna
- Atlantic mackerel (*)
- Mussels (*)
The highest methylmercury levels are found in large, long-lived fish. Therefore, pregnant or breastfeeding women and young children should not consume the following:
- King mackerel
- Bluefin tuna
You can find a list of various fish, their omega-3 content, their average mercury levels, and other contaminants in the article Fish Intake, Contaminants, and Human Health: Evaluating the Risks and the Benefits.2 The FDA also keeps a database of the average mercury concentration in various fish and shellfish species here.3
4 Health Benefits of Seafood
Certainly, the most obvious way to avoid the risks from eating seafood is to simply avoid it completely. But is that the wisest choice?
The fact is, seafood is packed with many important nutrients that many people are lacking in their diet, such as:
- High-quality protein
- Essential trace elements
- Fat-soluble vitamins (Vitamin D)
- Essential fatty acids (particularly of long-chain polyunsaturated fatty acids (LC-PUFA))
Let’s look at how some of these nutrients may benefit your health.
1. Seafood and Cardiovascular Disease
Although many of the above-mentioned nutrients can be obtained from other foods, seafood is the main source of LC-PUFAs. You may be more familiar with the two major classes of LC-PUFAs — omega-3 and omega-6 fatty acids.
Both types of essential fatty acids (EFAs) are thought to play important roles in the body. However, while omega-6s can be readily obtained from plant sources, the dietary supply of omega-3 is more limited, except when it comes to seafood.
One of the most well-known benefits of omega-3s is their association with a lower risk of cardiovascular disease. Specifically, two types of omega-3s, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been shown to be incorporated into blood vessel tissue, where they influence cell membrane fluidity. Numerous studies have suggested that such anti-arrhythmic effects could reduce the risk of coronary heart disease2 and sudden cardiac death.
2. Seafood and Infant Health and Neurodevelopment
Let’s talk about mercury. Yes, it’s true that mercury — in its organic form, methylmercury (MeHg) — accumulates in fish and other seafood. And acute mercury poisoning can cause neurological problems, particularly in fetuses and children.
However, this does not mean that anyone, including pregnant women, should eliminate seafood from their diet. In fact, avoiding seafood during pregnancy could backfire.
Numerous studies have suggested that maternal seafood and omega-3 intakes can have positive effects on various infant health and development outcomes, such as:
- Birth weight
- Length of gestation
- Visual development
- Cognitive development
One study indicated that maternal consumption of at least 8 ounces per week of seafood during pregnancy and breastfeeding was associated with improved visual motor skills in their children.3
Other controlled trials have demonstrated independent beneficial relationships of seafood consumption during pregnancy with language comprehension, higher IQ, visual recognition memory, etc. Such effects are likely due to the incorporation of DHA into the rapidly developing brain of infants during the last trimester of pregnancy as well as during the baby’s first two years.
Additionally, most species of seafood contains several other brain-selective nutrients that are essential for human brain development. At a minimum, they include the following:
Still, the methylmercury content does mean that young children and pregnant or breastfeeding women should practice discrimination in their choice of seafood. Because methylmercury concentrations increase as you go up the food chain, certain fish species should be avoided. A list of fish that should be avoided is included in the “Special Considerations” section below.
3. Seafood and Cancer Prevention
The omega-3 content of seafood has some scientists thinking that they may help prevent certain types of cancer. Omega-3s are well-known for their anti-inflammatory properties, and laboratory studies have shown that they can also increase the sensitivity of tumor cells to conventional therapies and induce apoptotic cell death.4 These LC-PUFAs also appear to have selective cytotoxicity against cancer cells, which means that they can target cancer cells without damaging or killing healthy cells.5678
However, it may be a bit too early to get excited about the prospects of omega-3s in cancer prevention. While some observational studies have shown that higher intakes and/or blood levels of omega-3s are associated with lower risk of certain cancers like breast9 and colorectal cancers,10 others have found no such relationships. Some have even indicated that omega-3s may increase the risk of certain cancers.
Overall, the data from existing studies show an inconsistent relationship between omega-3s and cancer risk. We will need to wait for results from additional clinical trials to help clarify this relationship.
4. Seafood and Vitamin D
Vitamin D, better known as the “sunshine vitamin,” is actually a steroid hormone that is produced by the kidneys and is required to control blood calcium levels. It is important for a number of reasons, a few of which include:
- Mineralization of bone, which keeps bones strong and healthy
- Helps regulate adrenaline, norepinephrine, and dopamine production in the brain
- Mood regulation
- Regulation of insulin levels, diabetes management
- Support for the immune, cardiovascular, and nervous systems
Unfortunately, an estimated 41.6% of the U.S. population has vitamin D deficiency,11 which has been linked to several chronic conditions like hypertension and type 1 diabetes.
But can’t you just spend some time in the sun to get your vitamin D?
That’s somewhat true. Sunlight is the primary source of vitamin D3, a variants of vitamin D. And many people may meet some of their vitamin D requirements this way. However, increased melanin absorbs and scatters ultraviolet rays, which results in reduced conversion of 7-dehydrocholesterol to previtamin D3.12 For this reason, vitamin D deficiency is more common in darker-skinned individuals.
Thankfully, sunlight isn’t the only source of vitamin D. Fatty fish, such as tuna, mackerel, salmon, and sardines are great dietary sources of vitamin D. Experts recommend 600 IU of vitamin D daily for most adults, an amount easily fulfilled by 3 ounces of salmon or swordfish.13
8 Tips to Enjoy Seafood Safely
The conclusion is obvious. Seafood should be a part of your diet. But what can you do to make sure you and your family don’t get sick? Fortunately, there are simple steps you can take.
1. Buying Seafood Right
Fresh Fish and Shrimp
When buying fresh fish and shrimp, the FDA recommends that you should only buy them from reputable sources (i.e., supermarkets, seafood market, etc.). Be sure to look at the origin label — the more information, the better.
I recommend buying wild-caught seafood whenever possible, but if that’s not an option for you, try to look for the Best Aquaculture Practices (BAP)14 logo. BAP is a third-party aquaculture certification program that encompasses the entire seafood production chain, starting from the feed mill to your plate. By having the BAP logo, you can be ensured that the seafood was produced in a way that is:
- Considerate of the health of the animal and the consumer
- Socially responsible toward the people and communities farming and processing the seafood
- Respective and protective of the surrounding environment
Some packaging may have temperature indicators to show that they have been properly stored at a temperature below 40°F. If there is no such indicator, look for fish and shrimp that are refrigerated or displayed on a thick bed of ice (preferably encased or covered). Color alone is not a good indicator of freshness.
The following tips can help you make the best choice:
- Flesh should be shiny and firm, and gills should be red.
- Fresh fillets should have firm flesh and red blood lines. They should also have no discoloration or drying around the edges.
- The odor should be fresh and mild. Overly fishy smell indicates the fish is not fresh.
- Fish eyes should be clear and shiny.
- Shrimp, scallops, and lobster should have clear flesh and little to no odor.
- Do not purchase cooked seafood or smoked fish if it is displayed in the same case as raw fish. They are at risk of cross-contamination.
- Keep seafood separated from other foods in your cart and bags. It is best to pick up seafood last and store it in your refrigerator within 2 hours of purchase (1 hour if the outdoor temperature is above 90°F).
The FDA issued these guidelines for safely selecting shellfish:
- Look for a label on containers of live shellfish or shucked shellfish. These tags contain information about the product, including the processor’s certification number. This means that the harvest and processing of these shellfish were done in accordance with national shellfish safety controls.
- Discard any cracked or broken clams, oysters, and mussels.
- Live shellfish will close if the shell is tapped. If they don’t, do not select them.
- Live crabs and lobsters should have some leg movement. Since they spoil rapidly after death, do not select them if you don’t see leg movement.
- Ice crystals indicate that the product has been stored for a long time, or thawed and refrozen. Avoid any product with them.
- Check that packages are tightly sealed and that they are free of dents and tears.
- The flesh of frozen fish should be hard and not bendable.
- Although seafood frozen at or below 0°F should be safe indefinitely, check the expiration date to ensure the highest quality.
2. Storing Seafood Properly
Put fresh seafood on ice or in the refrigerator or freezer within 1 to 2 hours after purchase. The refrigerator temperature should be 40°F or below to prevent spoilage. Also, keep raw seafood away from other foods to prevent possible contamination from drips. If the seafood will not be consumed within 2 days of purchase, it is best to wrap it in plastic, foil, or moisture-proof paper or container, and store it in the freezer.
Live shellfish should be stored in the refrigerator. Place them in well-ventilated containers covered with a damp cloth or paper towel.
Frozen seafood should be stored immediately in 0°F or below until ready for use. Do not remove them from their original moisture-proof packages.
3. Prepping Seafood Safely
To thaw frozen seafood, place it on a plate in the refrigerator overnight. If in a hurry, place the product in a plastic bag and immerse it in cold water before cooking it right afterward. It may also be microwaved on the “defrost” setting.
Seafood should be cooked at an internal temperature of 145°F, which will significantly reduce the chance of foodborne illness. For fish, cook until the flesh is opaque and separates easily from the bone with a fork. Crabs, lobsters, and shrimp should also be cooked until the flesh is firm and opaque. Shells of clams, mussels, and oysters should open as they cook. Discard the ones that don’t open.
Spoiled seafood can have a sour, ranci, or fishy smell that intensify after cooking. If you notice any of these unusual odors, do not eat it. Any seafood that produces an ammonia odor should also be discarded.
4. Serving Seafood
Now that the prep work is done, it’s time to enjoy your seafood! To ensure an enjoyable experience for everyone, seafood should never be left out of the refrigerator for more than 2 hours (or for more than 1 hour when the temperature outside is above 90°F. Keep hot seafood hot and cold seafood cold. For example, if you’re serving cold seafood (ex: shrimp salad), keep it in the refrigerator or in a cooler if you’re at a picnic.
The FDA also recommends that consumers keep hot seafood under a heat source if it will be out for longer than 2 hours or discard it after 2 hours.
5. Cleaning Up
Ready to clean up? Be sure to wash hands, utensils, cutting boards, and plates thoroughly for at least 20 seconds with soap and warm water after handling any raw seafood. Kitchen sanitizers may be used on cutting boards and countertops for additional protection.
6. Special Considerations When Eating Seafood
As we’ve discussed in the benefits section, seafood consumption is more beneficial than not for pregnant or breastfeeding women and for children. For these individuals as well as older adults and persons with weakened immune systems, the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) recommends the following guidelines.
- Eat 8 to 12 ounces of seafood per week from the following list which are higher in EPA and DHA and lower in methylmercury:
- Canned light tuna
You can find a list of various fish, their omega-3 content, their average mercury levels, and other contaminants in the article Fish Intake, Contaminants, and Human Health: Evaluating the Risks and the Benefits.15
- The highest methylmercury levels are found in large, long-lived fish. Therefore, Pregnant or breastfeeding women should not consume the following:
- King mackerel
- Fish caught in local lakes, rivers, and coastal areas may have mercury or other contaminants. Check local fish advisories. If there is no advice available, you may eat up to 6 ounces (or 1 serving) per week of fish from local waters. You should avoid consuming any other fish that week.
- Raw or undercooked fish and shellfish (including sashimi) should be avoided.
- Refrigerated types of smoked seafood should also be avoided. These are usually labeled as “nova-style,’ “lox,” “kippered,” “smoked,” or “jerky.” The FDA guidelines state that canned or shelf-stable smoked seafood is acceptable.
7. When in Doubt, Throw it Out
If you are unsure of how long your seafood had been stored prior to cooking, it is always better to throw it away than to risk potentially serious foodborne illness.
8. Reconsider Raw Seafood
You may have heard of the old rule of thumb: Don’t eat shellfish in months that don’t have the letter R. In other words, you should avoid shellfish in the very months when they’re the most popular — May, June, July, and August.
Unfortunately, abiding by this rule will not guarantee that you won’t get sick. Neither will alcohol, lemon or lime juice, or hot sauce, contrary to popular belief. The only way to kill Vibrio vulnificus and other bacteria in seafood is to cook them thoroughly.
Eating Seafood is Safer Than Not Eating Seafood
With all the terrible news out there regarding contaminated seafood, it’s understandable that many people are becoming more wary of the potential harm. From flesh-eating bacteria to toxic chemicals that cause neurological problems, you may think that it’s best to avoid seafood completely.
However, as we’ve discussed in this article, the benefits of seafood consumption far outweigh the risks. Seafood contains many important nutrients, and as long as simple precautions are taken, there is no reason why you shouldn’t enjoy seafood as a part of a healthy, balanced diet.
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