Image shows an example of a stainless steel tumbler or flask
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Is Stainless Steel Safe to Drink From? Or For Cooking?

Last Updated on March 16, 2024 by Ecologica Life

In an era where health and sustainability go hand in hand, the choices we make in our kitchens go far beyond taste and convenience. Among the myriad options for cookware and drinkware containers, stainless steel stands as the epitome of durability and timelessness.

That said, many environmentally conscious and health-conscious consumers are beginning to ask: “Is stainless steel safe to drink from? Is it safe to cook with?” The answer may not be as simple as many of us think.

Recent studies and discussions have shed light on concerns about metal leaching – the migration of metals such as nickel, chromium, and iron from stainless steel into our food and drink. This phenomenon raises eyebrows, especially when considering those with sensitivities or the potential long-term health effects.

This article aims to peel back the layers of assumption and marketing to get to the heart of the safety stainless steel. I originally intended to include here an investigation into the environmental impact of stainless steel, but as this article has become so dense, we will publish that part elsewhere and provide a link to it here when it is published.

What is Stainless Steel?

First, what is stainless steel?

Stainless steel is a type of alloy made primarily from iron. It contains a minimum of 10.5% chromium and a maximum of 1.2% carbon. During its production, additional elements such as nickel, molybdenum, niobium, or titanium may be added to enhance specific properties.

It is worth noting that stainless steel accounts for 43% of the cookware market, highlighting its importance in culinary applications. 1,2

Types of Stainless Steel

Before we go any further, let’s look at the different types of stainless steel. Not all stainless steel is created equal. There are many different grades of stainless steel.

Grades 304 and 201 are the most commonly used for drinkware. 201 is cheaper but less corrosion resistant and rusts more easily than 304. This is because of the different levels of nickel and chromium found in these grades. You can see the differences in Table 1 below.

It should be noted that in common kitchen appliances you can also find grades 301, 316 and 430.

Table 1: Differences in stainless steel grades by their nickel and chromium content.

Grade 304 is sometimes called as 18/8 stainless steel. See if you can work out why from the table.

Grade 316 also contains 2% molybdenum, which is an essential trace mineral found naturally in food.

For a steel to be considered kitchen-grade, it must have a minimum chromium content of 16%. This is because chromium plays a crucial role in forming a passive layer of chromium oxide on the surface of the steel. This layer is thin, tough, and invisible, and provides protection against rust and corrosion.

Is Stainless Steel Cookware Safe? What the Science Says

Stainless steel is used in about 43% of all cooking appliances. It also appears that the demand for stainless steel tumblers (flasks) is increasing significantly.3,4,5

We wouldn’t be using stainless steel if the general perception was that it wasn’t safe and durable. However, there are concerns about metal leaching even in the context of beverages and that is what we will discuss in this section.

Metal Leaching in Stainless Steel Containers

Metal leaching occurs when the metal components of a container or cooking utensil leak into the food or drink they come into contact with. This is a concern because, depending on the metal in question, this process could result in someone having unsafe levels of a metal in their diet.

In the case of stainless steel, the metals of interest are nickel, chromium, and iron.

Overview of Relevant Studies

This article isn’t a comprehensive review of the literature on stainless steel, but we will examine some relevant studies. If you know of other studies that you think should be mentioned in this article, feel free to leave us a comment below.

Acidic beverages (Bassioni et al., 2015)

A 2015 study (Bassioni et al., 2015) indicates that when acidic beverages such as fruit juices are stored in stainless steel containers for 1-5 days, there is a significant release of nickel, iron, and chromium into the beverages. This study focuses on selected juices (lemon, orange, mango and strawberry) as they are considered to be aggressive to stainless steel due to their low pH ranging from 2.8 to 4.35.6

The study by Bassioni et al showed that storage of lemon, orange, mango, and strawberry in stainless steel cups significantly increased the leaching of chromium, nickel, and iron into the beverages.

Bassioni et al found that after 5 days of lemon juice storage in a 201-grade steel container, the intake of nickel, chromium and iron was found to be 3.96, 0.48 and 36.57 mg/person respectively. This intake is higher than the acceptable limit set by the World Health Organisation (WHO).

In the study, at least 1 mg of nickel was released after just one day of fruit juice storage (for lemon, orange, mango or strawberry). Lemon released the most nickel from the container, with a total of 4 mg released after 5 days.

Cooking with stainless steel (Kamerud et al., 2015)

Another study from 2015 looked at the leaching of nickel and chromium into tomato sauce during cooking. They found that new stainless steel cookware resulted in more leaching, but in general only small amounts (88 micrograms of nickel and 86 micrograms of chromium) were leached into the tomato sauce. The stainless steel grades used in this study were 304 and 316, which are the most commonly used for cooking utensils. However, the study did not look at iron leaching.7

When comparing these studies, the evidence suggests that we might expect much more leaching from lower grades (201) than higher grades (304 and 316) of stainless steel.

Whey protein (Atapour et al., 2019)

A noteworthy 2019 study provides valuable insights into the interaction between grade 316 and whey proteins, which are commonly used in protein drinks. Whey proteins increase metal leaching of iron, nickel, and chromium. However, the leached concentrations were all well below health recommendations.8

This study adds to the evidence that leaching occurs less at higher grades of stainless steel.

Health Guidelines and Metal Exposure

When discussing the safety of drinking and cooking with stainless steel utensils, we should consider the established health guidelines. The WHO and other health authorities have set specific limits for metals such as nickel, chromium, and iron.

Nickel

The WHO and other health organisations have set guidelines for the safe intake of nickel and chromium. For nickel, the tolerable upper intake level (UL) is 1 mg per day for adults. This level is considered the maximum daily intake that is unlikely to cause adverse health effects.

Nickel is often implicated in causing allergic skin reactions and is recognised as the leading cause of allergic contact dermatitis. Sensitivity to nickel affects a significant proportion of the population, with an estimated 8-10% of women and approximately 1.2% of men exhibiting allergic reactions to Nickel.

The acidic beverages study showed that lemon juice stored in grade 201 stainless steel was found to release nearly 4 mg of nickel after five days. This is well above the daily UL and may pose a health risk to consumers.

However, the cooking with stainless steel study showed that cooking in tomato sauce in grade 304 and 316 resulted in relatively safe levels of nickel leaching into the tomato sauce. This is supported by the whey protein study, which found that nickel leaching from grade 316 in the presence of whey was well below WHO recommendations.

Chromium

Unlike nickel, chromium does not have a universally agreed UL because of its essential role in the human diet (stimulation of protein, carbohydrate, and lipid metabolism) and its low toxicity in the trivalent form (chromium III). Cr III is also known for its protective effect against diabetes and arteriosclerosis in humans.9

However, excessive intake of chromium, particularly the hexavalent form (Chromium VI), is associated with adverse health effects. Cr VI is toxic and has been linked to an increased risk of cancer, particularly lung cancer.10

Even Cr III can be bad for you at high levels. Although no UL has been set for Cr III, it should be noted that the data are limited and that high intakes of chromium may have adverse effects.11 The Food and Nutrition Board of the Institute of Medicine has indicated that people with kidney and liver disease may be susceptible to adverse effects from high intakes of chromium.12 There are also some isolated case reports that suggest chromium supplements may cause weight loss, anaemia, thrombocytopenia, liver dysfunction, renal failure, rhabdomyolysis, dermatitis, and hypoglycaemia.13,14

The National Institute of Health (NIH) suggests that a safe dietary intake of chromium for adults and adolescents is between 25 and 45 micrograms per day. However, these levels may vary depending on individual health conditions and dietary requirements. The WHO has set a guideline for the maximum amount of chromium in drinking water at 0.05 mg/L, which is similar to the dietary intake recommended by the NIH.

The acidic beverage study showed chromium leaching at 10-40 times that set by the WHO guideline. Even the study done by Kamerud et al showed chromium leaching slightly higher than the WHO guideline.

However, it is unlikely that the chromium leached in these studies was chromium VI. In the context of stainless steel used for cookware or containers, Cr III is added to the alloy to enhance its properties. During the production of stainless steel, chromium combines with oxygen to form a thin protective layer of chromium oxide on the surface. This chromium (III) oxide layer helps prevent further oxidation (rust) and corrosion, making the material ideal for food contact and culinary applications.

It’s theoretically possible for chromium (III) to be converted to chromium (VI) under certain harsh conditions, such as exposure to strong oxidising agents at high temperatures. However, such conditions are generally not encountered in the typical use of stainless steel in household cookware or containers. The risk of chromium (VI) formation from stainless steel in domestic use is therefore considered to be very low.

The results from the acidic beverages study show that stored fruit juices can release between 10 and 40 times the recommended amount from 201 grade steel cups, with mango releasing the most. Although this isn’t the toxic form of chromium, it is still higher than the recommended daily allowance for Cr III. In light of this evidence, storing juices in grade 201 stainless steel cups should be done with caution, especially for people with kidney and/or liver disease.

Iron

Iron is an essential nutrient, and health organisations have set the Recommended Daily Allowance (RDA) for adults aged 19-50 years is 8 mg daily for men, 18 mg for women, 27 mg for pregnancy, and 8 mg for lactation.15

The UL for iron is 45 mg daily for all men and women aged 14 years and over. For younger people, the UL is 40 mg. Too much iron can lead to a condition called iron overload or haemochromatosis. This condition affects a number of organs and can cause conditions such as liver damage, diabetes, hormonal imbalances and even neurological effects.

Kamerud et al didn’t look at iron leaching. The whey protein study didn’t find significantly high levels of iron leaching from grade 316 containers. However, the evidence from Bassoini et al. suggests that high levels of iron leaching occur during prolonged storage of fruit juices in grade 201 containers. This could lead to potential iron toxicity in consumers.

Nutritional Perspective on Metals

There is another perspective on this issue that should be considered. Iron and chromium are essential nutrients, and this leaching could actually be beneficial, at least for people with low dietary intakes. The same can’t be said for nickel, which is a potentially harmful metal.

Larger studies should be carried out to investigate whether metal leaching could be, or is, beneficial in any case.

Stainless Steel Grades and Leaching

When it comes to the safety of using stainless steel for food and beverage containers, not all stainless steel is created equal. The composition of stainless steel can vary significantly, resulting in differences in its resistance to corrosion and, consequently, its propensity to leach metals into food and drink.

The grades considered here are 201 vs. 304 and 316.

304 and 316 stainless steels

Often considered the standard ‘food grade’ stainless steel, 304 contains higher levels of chromium and nickel than most other grades. 316 contains even higher levels of chromium and nickel than 304. The composition provides excellent resistance to corrosion and oxidation, making it an ideal choice for utensils, pots, pans, and containers.

The high chromium content forms a protective layer of chromium oxide on the surface, significantly reducing the risk of metal leaching. The evidence presented here suggests that there is limited metal leaching in these grades, although it may be worthwhile to test grade 304 against acidic beverages, we can use the study done by Kamerud et al as indirect evidence that at least less metal leaching occurs with this grade. The acidity of the tomato sauces ranges from 4.17 to 4.3 pH, which is significantly higher than the pH of some of the juices tested by Bassioni et al.

201 stainless steel

While 201 stainless steel is less expensive and still resistant to corrosion, it does not offer the same level of protection as 304. The evidence presented here suggests that 201 stainless steel should not be used to store acidic beverages such as fruit juices for long periods of time due to metal leaching into the beverages.

In Summary, is Stainless Steel Safe?

The evidence suggests a clear hierarchy within stainless steel grades, with higher grade alloys offering a greater corrosion resistance and therefore a lower propensity for metal leaching. This insight is not merely academic; it has practical implications for consumers who want to make informed choices about their cookware and drinkware.

Opting for higher-grade stainless steel where possible appears to be a prudent strategy to minimise potential health risks associated with metal ingestion.

However, more studies should be done to investigate the concentrations of metals leaching from different grades of steel containers in the presence of different beverages.

If you are concerned about metal leaching into your drinks, you can opt for tried and tested materials such as glass and ceramics. These materials have been used for thousands of years, so we know they can be trusted.

Stainless Steel Environmental Impact

We were originally going to talk here about the environmental impact of stainless steel compared to its counterparts, but as this article became so in-depth, we decided to split this into two articles. We will add a link here when we have published our assessment of the environmental impact of stainless steel.

References

  1. I. M, Bernstein, Handbook of stainless steels, New York, NY: McGraw-Hill, 1977 ↩︎
  2. T. Santonen, H. Stockmann-Juvala, A. Zitting, Review on toxicity of stainless steel, Finnish Institute of Occupational Health, Helsinki, Finland (2010). ↩︎
  3. “Stainless Steel Cups Market Report | Global Forecast From 2023 To 2031,” Dataintelo. Accessed 22/01/2024. Available at Dataintelo’s website. ↩︎
  4. “Stainless Steel Cup Market Report 2024,” Cognitive Market Research. Accessed 22/01/2024. Available at Cognitive Market Research’s website. ↩︎
  5. “Tumblers Market Analysis – 2030,” Allied Market Research. Accessed 22/01/2024. Available at Allied Market Research’s website. ↩︎
  6. Ghada Bassioni, Ali Korin, Alaa El-Din Salama. Stainless Steel as a Source of Potential Hazard due to Metal Leaching into Beverages. International Journal of Electrochemical Science, Volume 10, Issue 5, 2015, Pages 3792-3802, ISSN 1452-3981, https://doi.org/10.1016/S1452-3981(23)06580-X. ↩︎
  7. Kamerud KL, Hobbie KA, Anderson KA. Stainless steel leaches nickel and chromium into foods during cooking. J Agric Food Chem. 2013 Oct 2;61(39):9495-501. doi: 10.1021/jf402400v. Epub 2013 Sep 19. PMID: 23984718; PMCID: PMC4284091. ↩︎
  8. Masoud Atapour, Zheng Wei, Himanshu Chaudhary, Christofer Lendel, Inger Odnevall Wallinder, Yolanda Hedberg. Metal release from stainless steel 316L in whey protein – And simulated milk solutions under static and stirring conditions. Food Control, Volume 101,
    2019, Pages 163-172, ISSN 0956-7135, https://doi.org/10.1016/j.foodcont.2019.02.031. ↩︎
  9. Safe Upper Levels for Vitamins and Minerals. ↩︎
  10. G. Herting, I. Odnevall Wallinder, C. Leygraf. Corrosion-induced release of chromium and iron from ferritic stainless steel grade AISI 430 in simulated food contact. Journal of Food Engineering, Volume 87, Issue 2, 2008, Pages 291-300, ISSN 0260-8774, https://doi.org/10.1016/j.jfoodeng.2007.12.006 ↩︎
  11. Chromium, Fact Sheet for Health Professionals, NIH. ↩︎
  12. Institute of Medicine (US) Panel on Micronutrients. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington (DC): National Academies Press (US); 2001. PMID: 25057538. ↩︎
  13. Fowler JF Jr. Systemic contact dermatitis caused by oral chromium picolinate. Cutis. 2000 Feb;65(2):116. PMID: 10696566. ↩︎
  14. Vincent JB. The potential value and toxicity of chromium picolinate as a nutritional supplement, weight loss agent and muscle development agent. Sports Med. 2003;33(3):213-30. doi: 10.2165/00007256-200333030-00004. PMID: 12656641. ↩︎
  15. Institute of Medicine (US) Panel on Micronutrients. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington (DC): National Academies Press (US); 2001. Available from NIH website. ↩︎
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