Published on June 26, 2017

Could too much fish be causing her brain fog?Could too much fish be causing her brain fog?

Rachael Hull of Marstons Mills loves to eat fish, and lots of it. Over the past four to five years, her appetite for swordfish, in particular, became what she thought was a “healthy” addiction.

“I love the taste of it and I progressively ate more and more,” said Hull.

She thought nothing of buying three pounds of swordfish at the store, especially when it was on sale.

“I’d cut it up and cook it all at the same time so I would have a serving every day. That amount would last me about one and a half weeks. It was an easy meal; I didn’t really have to think about it. I just seasoned the fish and threw it on the grill or into the oven. Life was easy, I always knew what I was having for dinner,” she said. “I thought I was doing something healthy.”

What Hull didn’t realize is that swordfish contains methyl mercury, a toxic organic compound found in fish, according to the Environmental Protection Agency (EPA). Swordfish is one of the species that contains the highest amounts of this compound, according to the United States Food & Drug Administration (FDA). Others are tilefish (Gulf of Mexico), shark and tuna.

Hull had been seeing Karen Lynch, MD, a neurologist with Cape Cod Hospital, for a couple of years because she was diagnosed in 1992 with multiple sclerosis (MS). It is a chronic disease of the central nervous that occurs when your immune system attacks nerves and breaks down the protective sheath around the nerves.

This disease can cause many neurological changes, such as impaired vision, fatigue, memory loss, forgetfulness, confusion, muscles spasms, and weakness.

Worsening Symptoms

While fatigue and cognitive changes can occur with MS, Hull’s symptoms had been worsening over a period of eight to 12 months. She works as a full-time mail carrier for the United States Postal Service and found she would go home and sleep for hours after work.

She had trouble remembering faces, lost her thought in the middle of sentences and was having a difficult time with word retrieval.

“Vitamin D deficiency can lead to fatigue and memory issues,” said Dr. Lynch. But, as part of her assessment, she asked Hull about her diet.

“When she told me that she was eating fish daily, that was a red flag.”

Dr. Lynch called Hull to give her the results.

“I knew something was wrong,” Hull said.

The normal range for mercury is 0-9 ng/ml, according to Dr. Lynch, and Hull’s level was 43 ng/ml. All of her other blood work was normal.

High levels of mercury can cause symptoms including loss of peripheral vision, pins and needles feeling in the hands, feet and around the mouth, lack of coordination in movement, impairment of hearing, speech, walking and muscle weakness, according to the EPA.

Quit Cold Turkey

The treatment was complete abstinence from fish.

“I had to quit cold turkey,” said Hull. “My healthy drug of choice was fish and my favorite meal was fish, sweet potato and peas.”

All she could think about during her first few days of abstinence was how much she loved fish and how she had to replace it with chicken, beef and pork. She avoided the seafood counter at the grocery store all together.

Her craving for fish slowly subsided over the next few months.

“Over a period of four months, her fatigue, mood and cognitive symptoms subjectively improved and a repeat mercury level was 8.3ng/ml, a drop of 80 percent,” said Dr. Lynch.

When Dr. Lynch told Hull she could now eat fish twice a week, she was so excited that she had fish that night. But then she became hesitant to eat it more often because she wanted to make sure her short-term memory, face recognition and word recall completely returned before she started eating fish twice a week. She has since decided, with Dr. Lynch’s support, that eating fish twice a week will be safe for her. And she continues to slowly regain all cognitive function.

The Dietary Guidelines for Americans, 2015-2020 published by the U.S. Department of Agriculture (USDA) and U.S. Department of Health and Human Services (HHS) recommends eight ounces of a combination of seafood each week.

Dr. Lynch recommends eating fish in moderation.

“There is not great data about what level of consumption of fish containing mercury is safe,” she said.

“Fish consumption has increased over the past two decades as a result of studies that have repeatedly demonstrated the associations between eating fish and a reduced risk for heart disease, stroke, dementia and diabetes. Less attention has been paid to studies highlighting the risks of overconsumption, including neurological deficits, autoimmune, endocrine, and neoplastic disorders.

“I would like to see fish markets and fishermen play a more active role in educating their customers about what’s in their fish.”