10 Vitamins You Should NEVER Take

Eric Berg stresses that synthetic vitamin A is not the same as the natural form. The body must convert synthetic retinyl esters into active vitamin A, a process that is sluggish and allows the synthetic form to accumulate in the liver and adipose tissue, where it can become toxic. This toxicity can lead to birth defects in pregnancy and it antagonizes vitamin D and K2, causing bone loss and increasing fracture risk. Additionally, many skincare products include synthetic vitamin A; when UV radiation hits these, they can become carcinogenic. Berg points out that most big vitamin companies use these cheap synthetic forms because of profit margins. He urges viewers to read labels and get vitamin A solely from food sources like egg yolks, liver, and cod liver oil, which provide the active form without conversion risks.

Berg clarifies that beta-carotene is not vitamin A; it's a precursor that must be converted. While many believe beta-carotene supplements are the same as eating carrots, the synthetic version is derived from coal tar petroleum and behaves as a provitamin with a dark side. A major study found an 18% increase in lung cancer in smokers taking synthetic beta-carotene. Berg explains that smokers already have vulnerable lungs due to ongoing damage, and the synthetic compound seems to 'flip the switch' that activates cancer. Natural beta-carotene from whole foods does not carry this risk and is protective. He advises against synthetic beta-carotene entirely, and if you want vitamin A, get it directly from animal sources.

Berg explains that folic acid is the synthetic form of vitamin B9, distinct from natural folate. A large percentage of people have a genetic variation in the MTHFR enzyme that severely limits their ability to convert folic acid into the usable methylfolate. Consequently, when they supplement folic acid, it accumulates in the bloodstream, and this unmetabolized folic acid has been associated with elevated cancer risk and suppressed immunity. He advises that anyone taking a multivitamin or B-complex read the label for 'folic acid' and switch to one that contains 'folate' or 'methylfolate.' He also notes that many processed foods are fortified with folic acid, so those with the gene mutation may be unknowingly exposed. The safest approach is to consume folate-rich foods like dark leafy greens.

Berg highlights that the most common synthetic B12, cyanocobalamin, has 'cyano' in its name because it contains a cyanide group. While the amount is tiny, the conversion to active B12 requires glutathione, the body's master antioxidant. Consistent intake of cyanocobalamin can deplete glutathione, increasing oxidative stress. This is particularly concerning for smokers, who already have a cyanide load, and for people with genetic detoxification variants (like Berg himself). He notes that cyanocobalamin is widespread: in energy drinks, fortified foods, and cheap supplements. The natural form, methylcobalamin, is more bioavailable and stays in the body longer, and does not contain cyanide. His personal experience with DNA testing revealed poor detox pathways, reinforcing his decision to avoid all synthetic forms and rely on dietary B12 from red meat or liver.

Berg is astonished that many popular calcium supplements list calcium carbonate as the first ingredient, which is essentially powdered limestone. He argues that ingesting rock in such large amounts is unnatural and leads to ectopic calcification—deposition in arteries and kidneys—and directly increases heart attack risk. He emphasizes that in nature, we never consume isolated calcium; it comes with cofactors like magnesium. He strongly disputes the common advice of 10:1 calcium to magnesium, insisting on a 1:1 ratio. Without adequate magnesium, calcium cannot be properly regulated and can cause muscle tension, cramps, and cardiovascular events. He therefore recommends obtaining calcium from dairy products like cheese, yogurt, and kefir, or from leafy greens, and pairing any calcium intake with equal magnesium.

Berg considers iron supplementation particularly risky because humans have no active iron excretion pathway; it only leaves through blood loss (menstruation, donation). Therefore, men and postmenopausal women are at high risk for accumulation. He describes ferrous sulfate as like 'rust,' and notes that many processed foods are fortified with iron, further adding to the load. High iron stores are linked to oxidative damage and diseases like type 2 diabetes, liver cirrhosis, Parkinson's, and Alzheimer's. He also mentions hemochromatosis, a genetic condition affecting 1 in 200-300 people, where iron absorption is excessive, making even normal intake deadly. He adamantly recommends obtaining iron from whole foods like red meat and liver, where it is heme iron and less likely to overload, even for anemic individuals.

Berg calls magnesium oxide a 'really cheap form' that tricks consumers. Its extremely low bioavailability means you either get almost nothing or, if you try to take enough to reach a therapeutic dose, you provoke osmotic diarrhea and lose vital electrolytes. He explains the typical scenario: a person takes a 500mg oxide pill, gets only 20mg magnesium, notices no effect, so increases the dose, then rushes to the bathroom and depletes their mineral stores. This makes oxide counterproductive. In contrast, magnesium glycinate is highly absorbable and well-tolerated, delivering the proven benefits of magnesium: improved sleep quality, reduced cortisol (stress hormone), reduced muscle tension and cramps, and increased cellular energy. He strongly recommends spending the extra money on glycinate.

Berg explains that synthetic vitamin D2 is made by irradiating fungus or yeast with UV light. It is not as potent as the D3 produced in human skin from sun exposure or from animal sources. The conversion of D2 in the body to the active 1,25-dihydroxy vitamin D is less efficient. Furthermore, the transport carriage—vitamin D binding protein—has a lower affinity for D2, so it is not carried as effectively to the liver and kidneys for activation. As a result, D2 raises blood levels of active vitamin D much less than D3. Berg notes that D2 is commonly prescribed because it's a synthetic that can be patented, whereas natural D3 cannot. He emphasizes vitamin D's critical roles in immunity, bone health, and mood, and urges people to ensure their supplement is D3.

Berg brings up the issue of omega-6 fatty acids in supplements, like linoleic acid added to dog food or human products. He states that the average person in the US already gets 25-30% of total calories from inflammatory seed oils, leading to an omega-6 to omega-3 ratio around 25:1, when it should be 1:1. Omega-6 fatty acids are precursors to pro-inflammatory eicosanoids, while omega-3s are anti-inflammatory. Consuming any additional omega-6 in supplements is dangerous because it fans the flames of systemic inflammation. He tells people to eliminate seed oils and get their essential fats naturally from fish, cod liver oil, and grass-fed meat, which provide a healthy balance.

Berg acknowledges copper is an essential trace mineral but warns that the cheap forms often sold in high doses can be toxic. The delicate copper-zinc ratio is crucial: we need approximately 10 parts zinc to 1 part copper. Imbalance either way causes problems—high zinc depletes copper, and high copper depletes zinc. More alarmingly, excess copper shifts from being an antioxidant to a pro-oxidant, generating free radicals. There is growing evidence that copper accumulation in the brain contributes to Alzheimer's disease by promoting amyloid plaque formation and neuroinflammation; researchers are now calling copper 'the new aluminum' in that context. To avoid this, he recommends consuming copper from whole foods like shellfish and liver, or taking a trace mineral supplement that respects the natural ratio.

Berg explains that many people think beta-carotene is vitamin A, but it is not; it must be converted into active vitamin A. The synthetic form, derived from coal tar petroleum, behaves differently in the body. A large study mentioned found a significant increase in lung cancer among smokers who took synthetic beta-carotene. Berg hypothesizes that smokers' lung tissue is already damaged and vulnerable, and the synthetic compound flips a switch to activate cancer. In contrast, natural beta-carotene from whole foods like carrots is protective, though you would need to eat enormous amounts to meet RDA for vitamin A. The key takeaway is that synthetic versions can be pro-carcinogenic, not just ineffective, and this is rarely highlighted.

Berg describes picking up a typical calcium supplement and finding calcium carbonate as the first ingredient, meaning the majority of the product is literally rocks. He says this form can accumulate in the body, depositing in arteries (vascular calcification) and kidneys (stones), and notably increases the risk of heart attacks. He emphasizes that in nature, we never consume isolated calcium like this; it's always packaged with other minerals. He also stresses that calcium must be balanced with magnesium in a 1:1 ratio, and that many supplements grossly exceed that (some suggest 10:1 calcium to magnesium), which can induce magnesium deficiency. The combination of a poorly absorbed, rock-based calcium with an imbalanced magnesium ratio leads to health problems.

Berg explains that cyanocobalamin, the cheap synthetic B12 found in many supplements and energy drinks, contains a cyanide moiety. Although the amount is small, it requires glutathione to convert to active B12, thus depleting that antioxidant. He notes that smokers already have a cyanide burden from cigarette smoke. For someone like him with genetic variations that impair detoxification (as shown by a DNA test), the added cyanide from continuous synthetic B12 intake can accumulate and cause toxicity. His personal experience of discovering his detox pathway weakness has made him hyper-vigilant about any synthetic toxins, including this B12 form. He strongly recommends natural methylcobalamin, which stays longer in the body and doesn't include cyanide, and getting B12 from red meat or liver.

Berg acknowledges copper is essential, but warns against cheap versions taken in high amounts. He emphasizes the copper-zinc ratio: we need approximately 10 times as much zinc as copper for everything to function correctly. Without that balance, excess copper can oxidize and cause damage. Specifically, copper accumulation in the brain is now being linked to Alzheimer's pathology, including amyloid plaque formation and inflammation. He says the scientific community is calling copper 'the new aluminum' because both metals are toxic to the brain and associated with the disease. He advises obtaining copper from whole food sources like shellfish, liver, or dark chocolate, and if supplementing, only with a balanced trace mineral formula.

Berg states that magnesium oxide has only about 3% absorption, so a 500 mg pill yields just 15-20 mg of actual magnesium. When people realize they aren't getting the benefit, they often increase the dose, which pulls water into the colon via osmotic effect, causing diarrhea. That diarrhea flushes out other electrolytes, worsening mineral imbalances. He contrasts this with magnesium glycinate, which has 80-85% absorption and does not cause diarrhea, providing reliable benefits like improved sleep, lower cortisol, less muscle spasms, and more energy. The key insight is that the cheap oxide form not only fails to deliver magnesium but can cause further electrolyte depletion, tricking people into spending money on an ineffective supplement.