Understanding Tolerable Intake Levels for Nickel
Nickel is a naturally occurring metal found widely in the environment, including the soil, water, and air. As a result, it is a normal component of many foods. For the general population, consuming typical dietary amounts of nickel is not considered a health concern due to low absorption rates. However, tolerable intake levels have been established to protect against potential long-term and short-term health effects.
Tolerable Daily Intake (TDI) for Chronic Exposure
The European Food Safety Authority (EFSA) updated its risk assessment in 2020 and set a Tolerable Daily Intake (TDI) for nickel at 13 µg per kilogram of body weight per day. This level is based on animal studies and is intended to be safe for a lifetime of exposure for the general, non-sensitized population. The EFSA highlighted that for certain age groups, particularly infants and children, chronic exposure could potentially exceed this TDI, raising some health concerns. The U.S. and Canada also set Tolerable Upper Intake Levels (UL) for soluble nickel salts, with adults at 1 mg daily and lower amounts for children based on age.
Acute Exposure and Nickel Sensitivity
For individuals with a pre-existing nickel allergy, ingestion of certain foods or water can trigger a systemic reaction known as Systemic Nickel Allergy Syndrome (SNAS). This can cause a flare-up of contact dermatitis (eczema), and in some cases, symptoms like headaches or gastrointestinal issues. The EFSA identified the lowest observed adverse effect level for nickel-sensitized people as 4.3 µg per kilogram of body weight for acute oral exposure. This means even small, single doses can cause a reaction in sensitive individuals.
Common Dietary Sources of Nickel
Dietary intake is the main source of nickel exposure for the general public. The nickel content in food can vary significantly depending on soil composition and processing methods. In general, plant-based foods tend to have higher nickel concentrations than animal products.
Foods typically high in nickel include:
- Legumes: Soybeans, lentils, and chickpeas are notable sources.
- Nuts and Seeds: Almonds, cashews, and various seeds are often high in nickel.
- Chocolate and Cocoa: These products contain significant amounts of nickel.
- Grains: Oatmeal, whole grains, and certain flours are high in nickel, with polished white rice containing less.
- Leafy Greens: Some varieties like spinach and kale can contain higher levels.
- Shellfish: Certain seafood and shellfish have been shown to have elevated nickel content.
- Processed and Canned Foods: The nickel content of food can increase if it is processed or stored in cans, though the significance is debated.
Foods typically low in nickel include:
- Most Meats and Poultry: These are generally low in nickel content.
- Eggs and Dairy: Milk, cheese, and eggs are considered safe for low-nickel diets.
- Many Fruits and Vegetables: Most fresh fruits and vegetables are low in nickel, though some exceptions apply.
- Refined Grains: White rice and refined wheat products typically contain less nickel than their whole-grain counterparts.
High-Nickel vs. Low-Nickel Foods: A Comparison
| Food Category | Examples of High-Nickel Foods | Examples of Low-Nickel Foods |
|---|---|---|
| Grains | Oatmeal, whole wheat, brown rice | Polished white rice, cornmeal, cornflakes |
| Nuts & Legumes | Soybeans, lentils, almonds, cashews | Fresh meat and poultry, eggs, most dairy products |
| Confectionery | Dark chocolate, cocoa powder | Most fruits, low-nickel fruits |
| Vegetables | Spinach, kale, onions, dried beans | Potatoes, carrots, cucumbers, fennel |
| Beverages | Tea, coffee, soy milk | Water (if tap is flushed), milk, many fruit juices |
| Cooking Methods | Acidic foods cooked in new/scratched stainless steel | Cooking in ceramic, glass, or seasoned cast iron |
Managing Your Nickel Exposure
While dietary nickel is not a concern for most people, those with a known allergy or other sensitivities may need to take steps to reduce their intake. This should always be done under the supervision of a healthcare provider.
For Nickel-Sensitive Individuals
- Low-Nickel Diet: Dermatologists sometimes recommend a low-nickel diet for a trial period (typically 1–3 months) to see if symptoms improve. This involves avoiding or limiting the high-nickel foods listed above.
- Watch for Contamination: Be mindful of canned foods, which may have higher nickel levels due to leaching. Avoid vitamin supplements containing nickel.
- Iron and Vitamin C: Consuming iron-rich foods or vitamin C can help inhibit nickel absorption.
Cooking Practices and Cookware
Good quality stainless steel cookware is generally safe, as the amount of nickel leached into food is typically minimal. However, certain practices can increase leaching, especially for acidic foods like tomatoes.
- Condition your cookware: The highest levels of leaching occur in the first few uses of new stainless steel pots. Using and washing them several times can form a passive layer that reduces further leaching.
- Avoid acidic foods in stainless steel: For those sensitive to nickel, consider using glass, enamel, or ceramic cookware for acidic dishes.
- Use low heat: High temperatures can increase the rate of nickel leaching. Triply stainless steel or lower heat settings can help.
Water and Environmental Factors
- Flush your tap: Tap water can pick up small amounts of nickel from pipes and faucets. Running the water for a few seconds can flush this out.
- Be aware of other sources: Nickel exposure can also come from jewelry, cosmetics, and cigarette smoke. For sensitized individuals, managing these sources alongside diet is important.
Conclusion
For the vast majority of the population, normal dietary intake of nickel from food and water does not pose a health risk. Health authorities, such as EFSA, have set safe intake levels for chronic exposure. However, for the segment of the population with a nickel allergy (Systemic Nickel Allergy Syndrome), dietary nickel can trigger flare-ups of eczema and other symptoms. Managing intake for these individuals involves careful food selection, optimizing cooking methods to reduce leaching, and addressing other environmental exposures. A low-nickel diet should only be pursued with medical guidance. The key is understanding your personal risk and taking appropriate precautions to stay within safe consumption levels. Additional guidance can be found via sources like the Human Health Fact Sheet 6: Low Nickel Diet for Nickel Allergic Individuals.
