What Is Nutrient Absorption, and How Does It Change with Age?

Written by Institute for Natural Medicine Staff

Medically Reviewed by Signe Poquette, ND

Published May 29, 2025
Last Updated May 30, 2025

Nutrient absorption is the process by which the digestive system extracts and transports essential substances into the bloodstream. From there, nutrients travel to the tissues and organs that need them most. This behind-the-scenes sequence comprises several steps:

Stomach acid helps dissolve and break down food.
Digestive enzymes from your pancreas and intestines break down nutrients into absorbable forms.
The small intestine, lined with tiny finger-like structures called villi, soaks up nutrients and passes them into circulation.
A healthy gut microbiome helps maintain balance and can even synthesize certain vitamins.

When everything is working well, your body efficiently turns food into fuel. But when one part of the system is off, due to stress, medication, age, or a poor diet, your ability to absorb nutrients takes a hit.¹ This can lead to deficiencies, even if you’re eating all the “right” things.

How nutrients are absorbed

Medical practitioner shows anatomical model of stomach

Chewing mechanically breaks food down and mixes it with saliva. This is your first digestive step, and it’s a crucial one. The more thoroughly you chew, the easier it is for your stomach and intestines to do their job.

In the stomach, hydrochloric acid and enzymes help release nutrients from food. The food then moves into the small intestine, where most absorption happens. Nutrients are taken up through the intestinal lining and transported across the body via the bloodstream.²

Certain nutrients need specific conditions to be absorbed efficiently:

Fat-soluble vitamins (A, D, E, and K) require dietary fat.³
Iron from plant sources (non-heme iron) is best absorbed with vitamin C.³
Zinc is affected by calcium intake. Too much calcium may reduce absorption.⁴
B12 needs stomach acid and a protein called intrinsic factor to be absorbed properly.⁵

How supplements are absorbed

Many supplements pass through the digestive tract without being fully absorbed, especially when taken at the wrong time, in the wrong form, or as part of an ineffective combination. Supplements are most beneficial when taken with food (unless otherwise directed) and in bioavailable forms (like magnesium glycinate instead of magnesium oxide). To get the greatest benefit, they should also be paired correctly. Vitamin D goes best with K2,⁶ for example, and iron with vitamin C.³^,⁷

Calcium carbonate requires plenty of stomach acid. If you’re older or on acid-reducing medications, you might not absorb it well.⁷
B12 tablets may be poorly absorbed if you have low stomach acid or a condition like atrophic gastritis.⁸
Multivitamins that combine iron with calcium or magnesium may compete for absorption and limit their effectiveness.

Find a Naturopathic Doctor

Experience the benefits of personalized natural healthcare with a trusted, licensed naturopathic doctor in your area.

Find an ND

Why absorption gets overlooked

It’s easy to focus on what you eat, but how well your body absorbs nutrients from food is just as important, if not more so. Think of it like pouring water into a sponge. A new sponge will readily soak up nutrients, while a used, porous sponge might let most of the good stuff run off. Similarly, your body’s absorption capacity changes with time.

As we age, many of the systems responsible for nutrient absorption begin to decline.¹ Stomach acid levels drop, the gut lining thins, and populations of beneficial bacteria plunge. These changes make it harder for older adults to absorb nutrients like vitamin B12, calcium, and iron, even when their diets haven’t changed.

Natural ways to boost food and supplement absorption

You don’t need a medical degree to improve nutrient absorption. Many natural strategies support the body’s intrinsic processes. Adding healthy fats (like olive oil, avocado, or nuts) to meals helps you absorb fat-soluble vitamins (A, D, E, and K), while cooking veggies like carrots, kale, and sweet potatoes with a bit of fat enhances their nutrient bioavailability.³

Low stomach acid is a common cause of poor absorption, especially in older adults. Natural boosters, like a tablespoon of apple cider vinegar in water before meals, bitter greens (arugula or dandelion), and digestive bitters, release enzymes that may help.⁸

A healthy gut lining and microbiome are essential for absorbing nutrients. Fermented foods (yogurt, kimchi, kefir) and fiber-rich prebiotic foods (garlic, onions, oats) support the proliferation of good gastrointestinal flora. Minimize ultra-processed foods and added sugars, which can disrupt that balance.

With supplements, timing matters

Take iron and calcium at separate times to avoid competition.⁹
Take vitamin D and omega–3s with your fattiest meal of the day.³
Follow label directions, and consult a healthcare provider for personalized timing and dose.

How absorption changes with age—and what you can do about it

From infancy to older adulthood, digestive efficiency, enzyme production, and gut health all play a role in how well you extract nutrients from food and supplements.¹ But your body’s ability to absorb nutrients changes over time, much like metabolism or hormone balance. Understanding these shifts will help you adapt your diet and supplement choices to meet different needs at every stage of life.

Infancy to adolescence: laying the foundation

In early life, nutrient absorption is typically robust. Infants, children, and teenagers have strong stomach acid, an active microbiome, and a high metabolic demand for nutrients to support growth and development. During these years, nutrients like iron, calcium, zinc, vitamin D, and B12 are essential for building bones, supporting brain health, and fortifying the immune system. Although absorption is generally efficient during this phase, poor dietary habits and digestive issues can still impair function.¹⁰^,¹¹

Adulthood (20s to 40s): maintenance with modern disruptions

Absorption remains efficient for many adults, but modern lifestyle factors can interfere. High stress, low-fiber diets, processed foods, excessive alcohol or caffeine, and common medications like antacids or antibiotics can compromise the body’s ability to absorb nutrients properly. It’s not uncommon for adults to experience borderline deficiencies, especially in magnesium, B vitamins, and vitamin D. Targeted supplements can help fill gaps for people under chronic stress or those recovering from an illness as well as those who might not get adequate nutrients from diet alone (vegans, vegetarians, and plant-based eaters).¹^,⁹

Midlife (40s to 60s): the shift begins

Around midlife, many people notice subtle changes in digestion. A natural decline in stomach acid production and digestive enzymes means certain nutrients (mainly B12, calcium, iron, and magnesium) may not be absorbed as easily as before. This stage often brings hormonal changes as well, which can influence nutrient needs and metabolism.¹^,⁹^,¹²

For women in perimenopause and menopause, calcium and vitamin D become especially important for maintaining bone health. A combination of vitamin D3 with K2 supports both bone and cardiovascular health,⁶ while B12 and magnesium help maintain energy, mood, and sleep quality.

This is the time to focus on gut health. Some people benefit from digestive enzyme support with meals or taking small amounts of apple cider vinegar before eating to naturally stimulate acid and digestion.⁸

Older adults (65+): supporting the aging gut

As you age, stomach acid levels often decline (a condition called hypochlorhydria), making it harder to absorb nutrients like B12, iron, calcium, zinc, and protein. At the same time, digestive enzyme production slows, and changes in the gut microbiome and intestinal lining further impair absorption. Long-term medications and chronic health conditions can worsen these issues.¹³

Older adults are more vulnerable to deficiencies in B12, calcium, vitamin D, zinc, and omega–3s.¹⁰ Reduced energy production is also common, making nutrients like CoQ10 especially valuable, particularly for people taking statins, which deplete the enzyme.

Targeted supplementation can help offset these changes:

B12 may be better absorbed via injection than taken orally.¹⁰
Calcium citrate is preferred over carbonate for those with low stomach acid.⁷
Vitamin D3 paired with K2 improves calcium utilization.¹⁰
Omega–3s support brain and heart health, and high-quality probiotics can help restore gut balance and immunity.

Smaller, nutrient-dense meals eaten throughout the day are often easier to digest. Emphasizing cooked vegetables, lean proteins, and healthy fats can also make a big difference in how well nutrients are absorbed and used.

Nutrient testing and personalization

If you’re struggling with low energy, digestive issues, frequent illness, or other signs of poor absorption, nutrient testing is a smart next step. Simple tests for vitamin D, B12, iron, folate, and magnesium can uncover deficiencies that diet alone might not correct. With personalized changes to diet, daily habits, and supplementation, you can restore balance and strengthen your foundation for lifelong health.

Footnotes

1
Kassis A, Fichot MC, Horcajada MN, et al. Nutritional and lifestyle management of the aging journey: a narrative review. Front Nutr. 2023 Jan 24;9:1087505. https://doi.org/10.3389/fnut.2022.1087505
2
Sensoy I. A review on the food digestion in the digestive tract and the used in vitro models. Curr Res Food Sci. 2021 Apr 14;4:308-319. https://doi.org/10.1016/j.crfs.2021.04.004
3
Melse-Boonstra A. Bioavailability of micronutrients from nutrient-dense whole foods: zooming in on dairy, vegetables, and fruits. Front Nutr. 2020 Jul 24;7:101. https://doi.org/10.3389/fnut.2020.00101
4
Wood RJ, Zheng JJ. High dietary calcium intakes reduce zinc absorption and balance in humans. Am J Clin Nutr. 1997 Jun;65(6):1803-9. https://doi.org/10.1093/ajcn/65.6.1803
5
Alpers DH, Russell-Jones G. Gastric intrinsic factor: the gastric and small intestinal stages of cobalamin absorption. a personal journey. Biochimie. 2013 May;95(5):989-94. https://doi.org/10.1016/j.biochi.2012.12.006
6
van Ballegooijen AJ, Pilz S, Tomaschitz A, Grübler MR, Verheyen N. The synergistic interplay between vitamins D and K for bone and cardiovascular health: a narrative review. Int J Endocrinol. 2017;2017:7454376. https://doi.org/10.1155/2017/7454376
7
Kopic S, Geibel JP. Gastric acid, calcium absorption, and their impact on bone health. Physiol Rev. 2013 Jan;93(1):189-268. https://doi.org/10.1152/physrev.00015.2012
8
McMullen MK, Whitehouse JM, Towell A. Bitters: time for a new paradigm. Evid Based Complement Alternat Med. 2015;2015:670504. https://doi.org/10.1155/2015/670504
9
Russell RM. Factors in aging that affect the bioavailability of nutrients. J Nutr. 2001 Apr;131(4 Suppl):1359S-61S. https://doi.org/10.1093/jn/131.4.1359S
10
Mouchaileh, N. Vitamin B12 deficiency in older people: a practical approach to recognition and management. J Pharm Pract Res. 2023;53: 350-358. https://doi.org/10.1002/jppr.1897
11
Rivera JA, Hotz C, González-Cossío T, Neufeld L, García-Guerra A. The effect of micronutrient deficiencies on child growth: a review of results from community-based supplementation trials. J Nutr. 2003 Nov;133(11 Suppl 2):4010S-4020S. https://doi.org/10.1093/jn/133.11.4010S
12
Norman K, Haß U, Pirlich M. Malnutrition in older adults—Recent advances and remaining challenges. Nutrients. 2021 Aug 12;13(8):2764. https://doi.org/10.3390/nu13082764
13
Mohn ES, Kern HJ, Saltzman E, Mitmesser SH, McKay DL. Evidence of drug–nutrient interactions with chronic use of commonly prescribed medications: an update. Pharmaceutics. 2018 Mar 20;10(1):36. https://doi.org/10.3390/pharmaceutics10010036

This article is provided by

The Institute for Natural Medicine, a non-profit 501(c)(3) organization. INM’s mission is to transform health care in the United States by increasing public awareness of natural medicine and access to naturopathic doctors. Naturopathic medicine, with its person-centered principles and practices, has the potential to reverse the tide of chronic illness overwhelming healthcare systems and to empower people to achieve and maintain optimal lifelong health. INM strives to fulfil this mission through the following initiatives:

Education – Reveal the unique benefits and outcomes of evidence-based natural medicine
Access – Connect patients to licensed naturopathic doctors
Research – Expand quality research on this complex and comprehensive system of medicine

About The Author(s)

Writer

Institute for Natural Medicine Staff

Our dedicated content team of professional staff writers represents decades of experience covering essential natural health topics in an accessible, evidence-based, and engaging way. Guided by a shared passion for holistic well-being, each and every one of our writers strives to empower our readers to take charge of their health.

Supported by a rigorous fact-checking and medical editing process from licensed naturopathic doctors that examines the latest in peer-reviewed research, our team brings their in-depth knowledge of natural health practices into every piece of content we produce. We strive to be the gold standard for evidence-based natural medicine, providing trustworthy information and inspiring narratives to help you live your best health, naturally.

Explore Healthy Aging & Nutrition Articles

Explore

Consumer

Education

Awareness, Advocacy, &

Action

Professional Education &

Research

What Is Nutrient Absorption, and How Does It Change with Age?

In this article:

How nutrients are absorbed

How supplements are absorbed

Why absorption gets overlooked