Seafood delivers a combination of nutrients that affects nearly every major system in your body, from your heart and brain to your thyroid and eyes. It’s one of the few food groups that supplies long-chain omega-3 fatty acids, a complete protein source, and hard-to-get micronutrients like iodine, selenium, and vitamin D all at once. The U.S. Dietary Guidelines recommend at least 8 ounces of seafood per week for adults, and the reasons go well beyond general “healthy eating” advice.
How Seafood Affects Your Heart
The most well-established benefit of eating seafood is cardiovascular. The omega-3 fats in fish, particularly the types found in fatty species like salmon, sardines, and mackerel, lower triglycerides in your blood. Each additional gram of omega-3s per day reduces triglycerides by about 6 mg/dl, which adds up meaningfully if you eat fish several times a week over months and years. High triglycerides are a major independent risk factor for heart disease, so bringing them down matters.
Beyond triglycerides, omega-3s from seafood have direct effects on how your heart beats. Lab studies show they can stabilize heart rhythm, though proving this in real-world settings has been harder. The overall picture from large population studies is clear: people who eat fish regularly have lower rates of fatal heart disease. The effects on other cardiovascular events like stroke and heart failure are less definitive, but the triglyceride and heart rhythm benefits alone make seafood one of the most consistently supported dietary interventions for heart health.
What It Does for Your Brain
Your brain is roughly 60% fat by dry weight, and it preferentially uses the same omega-3 fats concentrated in seafood. This shows up in long-term cognitive health. A large meta-analysis pooling data from multiple studies found that people who ate the most fish had an 18% lower risk of cognitive decline, an 18% lower risk of dementia, and a 20% lower risk of Alzheimer’s disease compared to people who ate the least. These aren’t small numbers for a dietary pattern, and the relationship held up across different study designs and populations.
The mechanism is partly structural. Your brain needs a steady supply of omega-3s to maintain cell membranes in neurons, support signaling between brain cells, and manage inflammation. When omega-3 intake drops, your brain substitutes in other, less flexible fats that don’t perform the same roles as effectively. Over decades, this difference in membrane quality appears to influence how well your brain ages.
Effects During Pregnancy
Seafood intake during pregnancy has a measurable impact on a child’s development. A landmark study published in The Lancet, tracking over 11,000 mothers and their children, found that women who ate less than about 12 ounces (340 grams) of seafood per week during pregnancy were more likely to have children with lower verbal IQ scores. Mothers who ate no seafood at all had 48% higher odds of their child falling into the lowest quartile for verbal intelligence. Low intake was also linked to poorer fine motor skills, communication, and social development in the children.
The study’s most striking finding was that eating more seafood, even above the amounts some guidelines cautioned against at the time, was associated with better outcomes for children. The researchers concluded that restricting seafood during pregnancy could actually be harmful to fetal brain development, because the nutritional benefits outweigh the small risks from trace contaminants in lower-mercury fish.
Thyroid and Metabolism Support
Your thyroid gland depends on two minerals that seafood provides in unusually high concentrations: iodine and selenium. Iodine is the raw material your thyroid uses to build its hormones, which regulate your metabolism, body temperature, and energy levels. Seafood, including fish, seaweed, and shellfish, is one of the richest natural sources of iodine available.
Selenium plays a different but equally critical role. Your thyroid produces hydrogen peroxide as part of the hormone-making process, and selenium-containing proteins protect thyroid cells from being damaged by that same chemical. Selenium also activates the enzymes that convert your thyroid’s stored hormone into its active form, the version your cells actually use. Without enough selenium, this conversion slows down, and your thyroid has to work harder to maintain normal hormone levels. Fish, shrimp, and other shellfish supply both minerals together, which is part of why populations with high seafood intake tend to have lower rates of thyroid problems.
Protecting Your Eyes
Age-related macular degeneration is the leading cause of vision loss in older adults, and fish consumption is consistently linked to lower risk. A pooled analysis of multiple studies found that people who ate the most fish had a 21% lower risk of early macular degeneration and a 29% lower risk of the more severe late-stage form. Every 15 grams of daily fish intake (roughly one extra serving per week) was associated with a 13 to 14% reduction in risk. Fish intake also appeared to slow the progression of existing macular degeneration by about 27%.
The omega-3 fats in fish concentrate in the retina, where they help maintain the light-sensing cells that are most vulnerable to age-related damage. This is one of the clearer examples of seafood’s benefits being tied to a specific tissue that actively accumulates its key nutrients.
Vitamin D: A Rare Dietary Source
Most people get their vitamin D from sun exposure, and very few foods contain meaningful amounts. Wild-caught salmon is a notable exception, providing roughly 988 IU of vitamin D per 3.5-ounce serving. That’s well above the 600 IU daily target for most adults. Farmed salmon, however, contains only about 25% as much, averaging around 240 IU per serving. The difference comes down to diet: wild salmon eat smaller organisms rich in vitamin D, while farmed salmon eat commercial feed.
Not all oily fish are equal on this front. Mackerel, often listed as a top vitamin D source, can vary dramatically. Some tested samples contained as little as 24 IU per 3.5-ounce serving. If you’re eating seafood partly for vitamin D, wild salmon is the most reliable choice by a wide margin.
Mercury: Which Fish to Choose
The main safety concern with seafood is mercury, a heavy metal that accumulates in fish tissue and can damage the nervous system at high levels. Mercury concentrates as you move up the food chain, so larger predatory fish carry the highest levels. The FDA and EPA jointly advise avoiding four categories: shark, swordfish, king mackerel, and tilefish from the Gulf of Mexico.
The “best choices” list, meaning fish low enough in mercury to eat two to three servings per week without concern, includes salmon, sardines, shrimp, tilapia, pollock, catfish, cod, clams, scallops, squid, trout, and many others. For young children, pregnant women, and nursing mothers, sticking to this lower-mercury group is especially important, since developing brains are more sensitive to mercury’s effects. The practical takeaway is that mercury risk is highly species-specific. Choosing the right fish lets you get the benefits without meaningful exposure.
What About Microplastics?
Microplastics have been detected in seafood, and this understandably concerns people. Tiny plastic particles have also been found in human blood, urine, and organs. However, the FDA’s current position is that the levels of microplastics detected in foods, including seafood, do not pose a demonstrated risk to human health. Some laboratory studies have suggested potential effects, but these haven’t translated into evidence of harm at the concentrations people actually encounter through eating. This is an area where the science is still catching up, but as of now, it does not change the overall recommendation to eat seafood regularly.