Magnesium is the second most common deficiency after Vitamin D. A magnesium deficiency can be a major cause of insulin resistance, making it easier to gain unwanted weight. Many of those entering their 30s will also experience a higher amount of stress, due to work and starting a family for example.

Since stress depletes magnesium levels in the body, supplementing with a high-quality magnesium supplement will benefit many aspects of your health, including sleep, stress and body composition.

Vitamin D is also essential. Deficiencies often stem from spending too much time indoors, without much exposure to the sun. Taking a vitamin D supplement can increase testosterone levels, which has a positive effect on body composition.

High amounts of chronic, systemic inflammation as we age are correlated to various diseases. Stocking up on fish oil is a great way to counteract this, as it acts as a powerful anti-inflammatory agent. Its benefits also extend to brain health, heart health and mood.

Since sleep issues are also common after the age of 40, having a dose of melatonin will be useful to some of those in their 40s. Melatonin is also a powerful antioxidant with neuroprotective benefits.

Similar to fish oil, curcumin has a very powerful anti-inflammatory effect. As we age, we tend to deal with more pains and aches, especially in our joints. Curcumin can help soothe these while reducing systemic inflammation that can cause diseases later on in life.

Since curcumin is not absorbed well by itself, it's important to choose one that is combined with black pepper or phospholipids (such as Meriva). Take it with fish oil for maximum benefit.

A great way to take care of many deficiencies at once is by taking a vitamin B-complex supplement. B-complex must be taken in the morning as it can increase energy levels. Since energy levels tend to be on the decline as we age, B-complex is great for a quick boost in the mornings.

See also: 5 Essential Nutrients For Plant-Based Diets